Yesterday upon the stair I met a man who wasn't there. He wasn't there again today Oh how I wish he'd go away.
— Hughes Mearns
Life is going good. Oh, okay — you might be a little stressed out or a little down in the dumps but it's nothing serious. Then things start going wrong. You see a face on the outside of a ten-story window; an impostor seems to be taking your place at home; the same white-eyed man keeps watching you from a distance; a tramp gives you proof that your neighbor is a demon, but the proof disappears soon after (as does the tramp).
You try to gather proof, you try to convince your wife, but she doesn't believe you. None of them believe you. They say you're crazy, but you're not crazy. Not at all. It's them making everyone think that. And they replaced your wife with one of them, so you had to kill it. You wouldn't kill your wife, would you? Would you? Of course not. It's all real. It has to be, because otherwise you'd be seeing Through the Eyes of Madness.
The creepy, foul-smelling uncle of the Cuckoo Nest, this trope makes a point of obscuring the objective truth of the tale in order to screw with the audience's minds. Sure, we see the grotesque tendril moving under the neighbor's skin just like the protagonist does, but who says the camera is telling the truth? Then again, there's never any conclusive proof that he's not a monster either. By their very nature, these stories end without any definite decision as to what was really going on.
Compare to Only Sane Man; in it the Only Sane Man, along with the audience, is sure that the strange thing is real and everyone else just turns a blind eye on it, while this leaves it ambiguous. Another key difference is that trope is often used for comedic effect while this trope is horrific if done properly.
Unlike the Cuckoo Nest, there isn't an "either/or" pair of realities that can be switched between, or a truthful reality waiting to be accessed — just a long, horrible descent into the darkness of the human mind.
Compare Unreliable Narrator, for instances in which this character is telling the story. Is often Paranoia Fuel at its purest, if done well. Contrast Maybe Magic, Maybe Mundane. If madness gives a person the ability to see real things that others can't, that's a variety of Power Born of Madness.
If it's clear that it's not all in the protagonist's mind and the danger is real, then the main character is Properly Paranoid. If the madness conceals the fact that the protagonist is a murderer, that's The Killer In Me.
Expect some spoilers here. In many works, the fact that the viewpoint character is crazy is a major Twist Ending.
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Paranoia Agent, a series directed by Satoshi Kon, starts off here, with the existence of Lil' Slugger and the sanity of the witnesses and/or victims in extreme doubt. When incontrovertible proof is presented that Lil' Slugger is real - but not a real person - and he is most definitely supernatural, that's the signal for things to really go off the rails.
Another of Kon's works, Perfect Blue, has this among the many tricks it plays with perception and reality. Towards the end, the audience is seeing things through the eyes of two different characters' madness, at the same time.
Paprika is another example. Once again, it's made by Satoshi Kon.
Ghost in the Shell has one of these. An assassin is interrupted by the protagonists, but blows himself up to take out his target Well, actually not. That minute of footage was all from his viewpoint, so he only thought he pulled it off. It's subtle to catch too, reading the revealing line wrong makes it look like there was some Deus ex Machina going on.
There was another episode focusing on a pilot fantasizing about assassinating his politician boss. It opens with a shot of him succeeding, then cuts to reveal that they hadn't gotten to the destination that it took place in. The main characters are randomly different people, apparently running a brothel. At the end, they agree that he's not a real threat to anyone's life, as he would never really go through with his assassination plot.
In Soul Eater, the effects of the Kishin and the Black Blood are an erosion of sanity. Since the good guys failed to stop the Kishin from reviving, the effect is slowly spreading over the entire world.
For examples, there's the kids hallucinations when they come face-to-face with Asura, Eruka and Free having the skin pulled off their faces plus the one where Black Star appears to succeed in stopping Eruka. Maka's hallucination in the Clown chapters is just cruel, twisting a cute flashback into the abrupt 'deaths' of her father and friends. One of the last battles in the series turns this around, with Stein hallucinating that his bloody killing of the enemy forces is, in fact, him 'unwrapping presents' to see what's inside.
Boogiepop Phantom plays out like this for the first few episodes (and probably longer than that even...) as most of the time the viewer's in WTFland trying to figure out what's real and what's not. Is that guy eating bugs for reals or is it just a sick illusion?
The final episodes for Neon Genesis Evangelion definitely qualify. Were the events of the last two episodes real, or were they all merely taking place in Shinji's shattered psyche?
From a literal standpoint, they could of potentially fit in during the closing moments of the Movie. Aside from a few completely minor details, the two endings are basically compatible with each other. Depending on your interpretation, of course.
In The Horror Mansion, the story "The Magic Ball" has an ugly scene at the end that shoves the entire story firmly into this camp. Despite previously seeing the hand of Atsuko's baby, indicating that it was a normal human child, we now see it as a monster, just like Mayako's babies... while Atsuko seems to see all the babies as normal. As Atsuko never seemed to have been affected by whatever the Magic Ball had done, this calls our vision of the babies as monsters into doubt. And if we can't trust what we see or read to be what really happened here, how can we know that any of the apparent strange happenings throughout the story were real? The monsters in the well, Isamu's transformation, the bizarre change in attitude of Mayako and Atsuko's parents... it's possible none of it was real.
The Filth, written by Grant Morrison, is deliberately ambiguous about how many of the events are real and how many of them are Greg Feely's encroaching madness.
In How Loathsome, Nick — a drug dealer — tells a story of how three German men followed him around, using mind-control powers to mess with his perception until he shot them dead. How much of this was a hallucination caused by drugs, how much is the truth and how much is a lie is never explained.
They throw me out, and I had a wife and an unborn child… or it was two cows and a goat? Sometimes it's so confusing…
Scott Pilgrim and Gideon Graves both subconsciously create false memories so they don't have to live with their mistakes. The false memories they come up with are kind of... weird, usually reducing the women around them to vapid, smiling fangirls who hang on their every word.
Whenever Deadpool is the main character or narrator. His main series that debuted in Secret Invasion is a great example, mainly the first issue showing him seeing the people trying to kill him as admiring fans wanting an autograph. He snaps out of it, but it makes you wonder just how reliable his point of view actually is. I mean, he thinks Nick Fury is a talking baby.
An issue of Ultimate Spider-Man shows the conversation between Spider-Man and Green Goblin from the previous issue, only from the latter's point of view. Among other things, he sees blood-red skies, Spider-Man as some horrifying human/spider hybrid (complete with fangs) and dozens of ghost-like "plasmids" floating around and whispering to him.
An issue of X-Men shows the final "Everyone against Cyclops" battle from Avengers vs. X-Men from Scott's point of view, while he's Drunk on the Dark Side of the Phoenix Force. He can't keep track of what's happening now as opposed to his memories (admittedly, at least partly because "a man with claws is attacking me" is a recurring theme), or whether he thought about doing something and decided not to, or did it and then used his Reality Warper powers to undo it again.
The realization that Nina from Black Swan is batshit insane puts an interesting spin on much of the rest of the movie.
The film from which this trope previously took its title, In the Mouth of Madness, was heavily inspired by the Cosmic Horror Story of HP Lovecraft and featured Sam Neill going mental with an axe. To make it even better, the question isn't just limited to whether Sam Neill's character is sane or not, but also whether he actually exists or is just a figment of the in-story horror writer's imagination (or for that matter, a figment of the screenwriter's mind). The man's not just in the mouth of madness, but being digested.
In Total Recall (1990), the main character is either a secret agent in deep undercover on Mars (which is what he paid Rekall to experience), or he is going insane due to brain damage from side effects of the memory implant.
The Amityville Horror is one of the best examples, especially the remake. The protagonist becomes possessed by the haunted house, seeing his own children (and wife) as demons and eventually killing his own dog with an axe! Later on he goes after the family too, but after being knocked out and dragged away from the house, he becomes sane again.
The Machinist is an almost surrealist example of this trope. However, the ending revelation rationalizes everything.
Jacob's Ladder, where the main character can't tell whether he's really switching back and forth between realities, or if the hellish experiences and the crazy Government Conspiracy he thinks he went through are just the products of his feverish mind. It turns out he's dying and/or in purgatory, and all the awful things he goes through are helping him let go of his life.
Vanilla Sky (2001), directed by Cameron Crowe and starring Tom Cruise. Remake of 1997 Spanish film Abre los Ojos, a.k.a. Open Your Eyes. After a car accident that kills his girlfriend and disfigures his face, the protagonist is haunted by increasingly bizarre occurrences. The ending explains that everything that has occurred after the car accident has been a dream. In real life, after the car accident, he signed a contract with a company that preserves its clients' bodies after death and keeps their brain waves active in lifelike virtual reality dreams, and then committed suicide. The bizarre occurrences are explained as glitches in the program. In the end, he decides to wake up from the dream program.
In The Tenant, the protagonist (played by Polanski) learns that the previous tenant of his apartment had committed suicide by throwing herself from the apartment window; he becomes convinced that his neighbors are trying to force him to re-enact her suicide. By the end of the film, it is unclear how much of what we have seen has been the product of his descent into madness.
Since The Descent's main character was hallucinating without a doubt at several separate points, there is a popular theory that the cave monsters were all in her mind and it was her that killed all her friends. The director originally put a crawler silhouette into the first hallucination sequence (which took place outside the cave) but had it edited out because he wanted to leave it more ambiguous.
American Psycho seems just about plausible as a conventional serial killer movie — until the Villain Protagonist goes to withdraw money from an ATM and it displays a message that he finds perfectly reasonable: "FEED ME A STRAY CAT."
The end of the film reveals that one of his victims was alive and well all along, and the "murder scenes" were just violent doodles he drew in his notebook.
The original Koji Suzuki short story just about counts as this trope, too. Yoshimi experiences several minor paranormal occurrences, and at the end is unsure whether it was real or the product of her over-stressed mind.
Stanley Kubrick noted with the film The Shining that it was his objective to create this impression instead of supernatural powers being at work (for instance, it's suggested that the locked storage room's door accidentally went open, not due to any ghosts). There were still some details that couldn't be explained by assuming the protagonist(s) are crazy, especially "the shining" psychic powers used by Danny to call Hallorann for help even though he's hundreds of of miles away.
La Moustache, a minor French film, uses this to a smaller degree. First the protagonist shaves off his moustache, and his wife doesn't remember he ever had one. He finds photos of a vacation they took, and in the photos he had a moustache, but the photos disappear, and his wife doesn't remember ever taking the trip. Then he tries to call his mother and finds out she's been dead for a year, and his wife tries to have him institutionalized and forcibly medicated. He escapes and flees to another country, gets a hotel room and wanders around for a while—then returns to the hotel room and discovers his wife's there, and thinks they're on vacation together. She doesn't remember any of his previous confusion, and the viewer is confused in turn.
The Hand wherein the protagonists severed hand goes around killing people. Turns out it was him all along doing it because the trauma of losing his hand and finding out his marriage is very unstable drove him insane.
'Spiral', which leaves several questions up in the air at the end. Did he kill all of these women? Did most of them actually exist? What's the final sketch?
Inland Empire, like most of the movies of David Lynch, starts in a somewhat "realistic" way, but after the first hour, is practically impossible to know what thing is real, a dream, or hallucinations.
The war of wills between the title character and the housewife in Peter Weir's The Plumber has some elements of this. Certainly, the plumber does behave in ways that are completely inappropriate and occasionally illegal, but the film keeps it deliberately vague as to whether he's a genuine psycho who is menacing this poor woman, or she's a neurotic who is projecting her anxiety onto a harmless oddball.
In Dont Look Back, the viewer sees things from the point of view of main character Jeanne, who increasingly comes to doubt her own sanity as the film progresses.
In Summer Of Sam, there's a scene of David Berkowitz being ordered to go out and kill people by his neighbor's demon-possessed dog. (Also historically wrong, as the real Berkowitz eventually admitted he'd made up the demon-dog story when he was bucking for an insanity defense.)
In the original version of Cat People, whether the wife was really turning into a vicious beast or was just plain nuts was left heavily ambiguous, until the final scene.
In Clean, Shaven the protagonist is a man suffering from schizophrenic, and it uses abstract images and sounds to show what he is experiencing.
In Eden Log, the man perceives the rape attempt as if he is making love with the botanist. We are shown what is happening from his warped perspective, interspersed with shots of him violently attacking and about to rape the woman.
In the first Spider-Man movie, Norman Osborne hallucinates first the Green Goblin mask and then his own reflection talking to him, symptomatic of his split personality brought on by the serum he injected. At the end of Spider-Man 2, Harry hallucinates his father in the mirror, telling him to avenge his death. Harry breaks the mirror and finds a room full of serum... Spider-Man 3 has Harry suffering two hallucinations; a further hallucination of his father (though judging by the voice it's more like the Green Goblin than Norman) representing his evil side, and Bernard, his butler, who Word of God says is a hallucination that represents Harry's good side.
Scott Pilgrim vs. The World. Though fans are divided on how to interpret it, Word of God from the director says that most of the weirder stuff that happens in the movie is all in Scott's head, and none of it actually happened. A popular fan theory is that Scott is actually a deranged serial killer. The movie also frequently has weird scene transitions (and weird scenes in general) that make it very hard to tell which parts are really happening and which parts are Scott's daydreams/actual dreams. For example, there's one scene where he excuses himself to go to the bathroom. After doing his business as normal, he exits the bathroom, only to find himself in a corridor resembling a school corridor. He follows it to the end to see his own front door, with snow in front of it, and Ramona standing in front of it ringing the doorbell. The doorbell ringing gets louder and louder, until the scene fades into Scott waking up in bed with the doorbell ringing for real. Just what happened between the bathroom scene and the dream?
Fight Club deals with a nameless protagonist befriending a man named Tyler Durden and creating an underground fighting ring for men. As it turns out, Tyler is merely a split-personality that represents the kind of person the narrator wants to be, which means for the majority of the film he's talking to himself.
In Hellraiser: Inferno, Joseph keeps seeing momentary visions of the Cenobites as people's faces randomly morph into nightmarish shapes. When Joseph confronts them they are perfectly normal however. The world around Joseph gradually becomes increasingly bizarre and nightmarish and it becomes unclear what is even happening for real. He's revealed at the end to not actually have been insane, but being tortured in hell for most of the movie.
Enemy: One popular interpretation of the film is that it takes place mostly in Adam's head, with Anthony being a symptom of his delusions.
Rachel Klein's The Moth Diaries... You never figure out how much was hallucination, or whether it was indeed hallucination at all.
A Scanner Darkly by Philip K. Dick. The protagonist has increasing trouble in making the distinction between reality and fantasy, due to his addiction to a drug that causes a split between the two hemispheres of his brain.
This is a favorite trope of Philip K. Dick and variations appear in most of his works.
PKD lives on this trope (this and Paranoia Fuel). VALIS, anyone? Flow my tears the policeman said, Game players of Titan, Ubik... hell. Pick any of his novels or short stories and you will find a protagonist spiraling into either the terrifying deconstruction of his own mind, or the painful deconstruction of reality. Either way, said protagonist is going to be royally screwed.
A Maze of Death isn't as well-known (understandably, due to its inconsistent publication history), but it's a pretty good rehearsal of the themes PKD would soon explore in more detail in Ubik.
This is explored in The Return, the final book of Blood Knight Rachel from the Animorphs series. Rachel is a character who has spent the past forty-seven books devolving from an Action Girl to a Blood Knight and Sociopathic Soldier. Consequently, a good chunk of this book focuses on hallucinations she's experiencing. Though, to be fair, a good deal of these hallucinations are induced by Crayak. The books deals with the return of David as well, and she continuously relives conversations she had with David internally. These conversations are shown in a font used nowhere else in the series, perhaps to underscore how badly Rachel is cracking up.
Lunar Park. The narrator is a writer named after the author of the novel: Bret Easton Ellis who is an unreliable narrator, because he describes things the other characters don't see or feel. The main character is abusing drugs, some of the hallucinations might be to some extent related to that. Also there is a intertextual reference to Ellis novel American Psycho. Ellis' character has apparently also written a novel titled American Psycho and he says: "Patrick Bateman is an unreliable narrator."
Germain, from Eric Nylund's A Game of Universe, has multiple personalities. However, he knows he has them (and can usually keep them in control) and there's a valid source for them: a magical ritual to copy knowledge from someone. However, when he learned the ritual no one mentioned the voices-in-your-head side effect, and coincidentally he doesn't start hearing them until after some incredible traumatic experiences. By the end of the story, two characters have suggested that he didn't actually copy their personalities into his head, he simply made them up in order to justify doing certain unpleasant things (however one of the characters advancing this idea lives in his head, and the other is a Mind Screwing telepath).
Shutter Island. Saying more about it would just spoil it, and it's worth reading.
Stephen King's The Girl Who Loved Tom Gordon plays this trope with one aspect. The creature that stalks Trisha, and eventually confronts her at the book's climax: is it just a black bear, distorted by her fear and her fever-induced hallucinations? Or is it really the supernatural horror, the "God of the Lost" she imagined it to be as it stalked her, and during her mental duel with it? Just to toy with you, the novel has someone else witness it who seems to provide the objective truth of it being a black bear... then it turns out he thought it was something else for a moment, too, and he's a drunk and no more reliable.
This comes up again in his short story "The Moving Finger", in which a man believes that he sees a finger sticking up out of his bathroom sink's drain. Things get increasingly weird (and the main character gets increasingly unhinged), until the reader isn't sure what's really going on. The ending suggests one possible 'mundane' explanation, but leaves it ambiguous.
This story can also be read without doubting the narrator, and either way the very end seems to be designed to suggest that it was all real.
Stephen King explores and discusses the trope more extensively in his short story "The Ballad of the Flexible Bullet". A writer is told a story by his publisher about another writer, struggling with writer's block, who became obsessed with the idea that his typewriter was inhabited by beings who were truly responsible for his writing ability, beings who needed to be appeased with offerings for his continued success. The protagonist indulges what seems like a harmless superstition by leaving an offering for the "Fornits", and gradually spirals into the same delusions. The climax in particular implies either that the writer was actually right, or had managed to thoroughly delude his wife who had, up until that point, seemed to be a non-believer.
King said that the appeal of The Shining, for him, was the way that it "blurred the line between the supernatural and the psychotic" — although it seems less blurry than in Kubrick's film version.
King also does this in his short story "Suffer the Little Children", in which neither the teacher nor the readers are sure if her students are "something else" or not. They seem to confirm their identity to her, but who knows if the words the teacher hears are what was really said?
Nick Cave's And the Ass Saw the Angel is really clever about this. The book quickly establishes the setting as a Magic Realist one. But then the protagonist turns out to be a pretty Unreliable Narrator, and we're left wondering how much is in his head.
Truman Capote's short story "Miriam" tells the story of a little girl taking over a middle aged woman's life. Except that the little girl exists only in the woman's head.
In House of Leaves, Johnny describes in detail how the Minotaur attacks and rips into him, or how he vomits at its stench, only it didn't happen and the creature was never there in the first place. Or was it? The book is irritatingly vague about whether the creature exists or Johnny is hallucinating. For certain, Johnny descends further and further into insanity as the book progresses.
"Young Goodman Brown", by Nathaniel Hawthorne, uses this. Goodman Brown is walking into a forest with the devil to a witch's meeting, at which he sees all the good and prominent people of his Puritan township in unholy worship. He ultimately rejects the devil and the whole thing disappears, leaving the reader and the character unsure of whether or not what he had seen was real. The lack of surety and the constant doubt poison Goodman Brown until he finally dies as a twisted, suspicious, lonely old man.
The Reveal in Evil Genius starts out sounding like Cadel is simply paranoid, but then the evidence starts stacking up...
"The Yellow Wallpaper" describes of a woman who's locked in a room with only the yellow wallpaper to look at, growing more obsessed and insane about it as time goes on. It's semi-autobiographical.
Several of H.P. Lovecraft's stories (notably "The Rats in the Walls") read in this fashion, it often never being quite clear whether what's happening to the characters is actually happening, actually happened, or whether the characters just went insane. The fact that many of them start off clearly not that well adjusted in the first place and even more of them wind up in an insane asylum or living deep in Paranoia Fuel Territory really doesn't help things.
Played with in The Temple, where the narrator is trying to tell his story while constantly pointing out that much of what he is writing is probably just delusions brought on by madness.
Dracula has a couple long stretches that read like this. Notably, Jonathan's diary entries get like this, especially if read taking into consideration exactly how his sense of time passing has been screwed up. It's definitely a viable Alternate Character Interpretation that the main cast are all pretty cracked.
"Relating the advent in France of an invisible being who lives on water and milk, sways the minds of others, and seems to be the vanguard of a horde of extra-terrestrial organisms arrived on earth to subjugate and overwhelm mankind, this tense narrative is perhaps without peer in its particular department."
The apparently boring narrator of Sarah Waters's The Little Stranger, who may or may not be responsible for all the horrible things that happen — including the suspicious death of his ex-fiancée.
Waters's earlier novel Affinity also featured a first-person narrator sliding into insanity, though there it's made quite clear at the end what's actually going on.
The short story "A Pursuit" by Brian Evenson. The narrator describes how for days he's been pursued by his third ex-wife, or maybe it's his second ex-wife, while sometimes interrupting himself to give a Suspiciously Specific Denial about the death of his first ex-wife or to criticize himself for Breaking the Fourth Wall. While the ending is very open to interpretation, it implies that he had already murdered all three of his ex-wives before the story began.
In Dean Koontz's Odd Thomas, this is partially used in the fact that it's made to seem that Stormy lives through the mass murder at the mall, when instead it's just Odd's ability to see dead people fooling the reader into thinking she's alive. Odd even says, "For a while I had gone mad."
In The Terror by Dan Simmons it's not clear if the monster slaughtering the explorers is just a combination of sleep deprivation, denial, stupidity and a bear or if it is actually the spirit Arctic.
One Flew Over The Cuckoo's Nest is narrated by "Chief" Bromden, a paranoid schizophrenic who hears machinery clanking in the walls, sees his fellow patients controlled like marionettes by Nurse Ratched, and repeatedly claims the entire ward is enveloped in a thick white fog that makes it impossible to see or move. At the beginning he claims that everything he describes "Is true even if it didn't happen."
His narration doubles both as a terrifyingly astute metaphor, and a description of his own view of a reality that was long ago fucked over.
A version of Hans Christian Andersen's "The Emperor's New Clothes" featured in one of the Datlow/Windling Whole Plot Reference collections plays a relatively lighthearted version of this. Due to a twist involving the boy who reveals that the Emperor has no clothes, both the narrator (The brother of the Emperor, who is a manipulative, treacherous would-be usurper who's far more incompetent than he realizes) and the reader are left wondering whether the clothes didn't exist, or they really did exist, and the narrator couldn't perceive them because he was wholly unfit for his position.
In Larry Niven's story "The Ethics of Madness", the protagonist unknowingly goes off his meds because his autodoc's "refill me" light burns out just as the drug supply is exhausted. Once, he uses another autodoc and gets re-medicated... and when it wears off, he "realizes" that the other autodoc had been tampered with by his "enemy". Not surprisingly, things go downhill from there.
The Doctor WhoEighth Doctor Adventures novel The Blue Angel is a less-disturbing variant than most: the Alternate Universe human Doctor has already been diagnosed as mentally ill, generally doesn't take his delusions too seriously, and generally stays on his meds, so it seems that he's unlikely to become too terribly confused. However, it does render the story very confusing, especially as some of the things he has delusions of certainly seem to be actually happening in one of the story's other plotlines, and the reader really can't tell if the story contains Magical Realism or the Doctor simply hallucinates that his mother is a mermaid, one of his friends has a talking dog which tells his other friend that all realities and stories are equally real, and other strange things. It also creates the impression that perhaps the TV series is basically All Just a Dream — the Doctor just has delusions about Daleks and Cybermen and weird phallic monstersmade of cellophane and such.
Patrick McGrath, author of Spider and The Grotesque, seems to be fond of this trope.
This trope is the only possible explanation for the Mind ScrewyGoosebumps book I Live In Your Basement, about a boy named Marco who defies his overprotective mother and goes out to play baseball, only to get hit in the head. While recuperating, he receives strange calls from a boy named Keith, who lives in his basement, and is said to be a blob monster disguised as a human. The rest of the story shows how Marco's reality is slowly slipping away and how everything he experienced is either a dream or a vivid hallucination — until it's revealed at the end that Keith is the one having the weird dreams and that he's the one who lives in fear of the human who lives upstairs.
Barry N. Malzberg's short story "What I Did to Blunt the Alien Invasion". This story has two tracks, one in which aliens reveal themselves to a man and warn of a coming invasion, after which he does everything within his limited means to warn people, including offering to betray humanity. The other is implied to be a man who becomes unstable, eventually causing his wife to leave and he to be arrested.
Alexandre Dumas's "The Woman with the Velvet Necklace" establishes early on that is viewpoint character comes from a family with a history of mental illness, and that he himself hasn't always got the stablest relationship with reality. Later, even the viewpoint character is tortured by the questions, is he going insane? Is he a recent escapee from a mental hospital? Or is the story that he's a recent escapee from a mental hospital merely a coverup for a story that is far more bizarre and horrifying?
The premise of Sheridan Le Fanu's short story "Green Tea". Is Rev. Jennings really being visited by a demonic monkey that no one else can see? Or is the green tea he drinks habitually slowly poisoning him, causing visual and auditory hallucinations? The story's narrator insists it's the latter, and is confident he can cure Jennings, but before he gets a chance to try, Jennings kills himself under the monkey's orders. It's made doubly tricky via its use of the Direct Line to the Author ploy: the story's "editor" freely admits to having changed the names of all the characters save for the protagonist, and tweaking and omitting bits of information here and there - but nevertheless insists he is completely impartial.
The Aunt's Story by Patrick White, which has three sections. In the middle one, the protagonist goes mad, and the reader gets seriously Mind Screwed.
Fight Club deals with a nameless protagonist befriending a man named Tyler Durden and creating an underground fighting ring for men. As it turns out, Tyler is merely a split-personality that represents the kind of person the narrator wants to be, which means for the majority of the book he's talking to himself.
Wilfred. The protagonist Ryan sees Wilfred not as a dog, but a man in a dog costume. Often, even though Ryan generally looks after Wilfred for a neighbor, the viewer can't always be sure if Wilfred's really there or not. And Ryan once spent an entire episode hallucinating in his basement, during which Wilfred and a passing stranger (who isn't really there at all) put him through various games. In another, Wilfred allegedly sneaks hallucinogenic drugs into his tea. This becomes a bit of fridge horror when one considers that Wilfred really is just a dog, meaning Ryan likely drugged it himself without even knowing. During the resulting drug trip, Wilfred murders Ryan's "spirit guide" to prevent Ryan discovering the truth about who/what/why Wilfred is. And in a recent episode, it's suggested Ryan somehow set himself up to be framed for mass money fraud without being aware and blaming it on Wilfred (it turns out Ryan's girlfriend was out of her mind and did it herself at the instruction of her own Wilfred hallucination - this one French). Couple all of this with the series' many dips into Ryan's past, revealing many dark and traumatic aspects of his life and psyche, and it can be very difficult to figure out which parts of episodes are real and which parts are just in Ryan's mind.
A seventh-season episode of CSI: Crime Scene Investigation danced around this trope, when the team gets to deal with a cult that believes in an Ancient Conspiracy of shapeshifting snake aliens. One of the cultists is under interrogation, and at one point we see the detective raise his water glass and, without warning, dip a snake-like tongue into it. Of course, this being CSI: Crime Scene Investigation and not The X-Files, this was only a hallucination of the cultist. Probably.
Subversion: the Star Trek: Deep Space Nine episode "Whispers", where everybody Miles O'Brien knows slowly turns against him. The subversion is that it is Miles O'Brien himself who has been replaced, and the story is told from the clone's point of view. He doesn't know this, but everybody else does (or learns). Both he and the audience only find out at the end.
In the episode "Persistence of Vision" on Star Trek: Voyager, Janeway is starting to see parts from her holodeck program in different parts of the ship. They go from little things, like being served the same meal as the one she saw in the program, to characters talking to her. It finally culminates into one of them attacking her in her quarters. She wrestles the attacker down and calls for security. Just as you're wondering what's taking security so long to get there, the camera shifts and it turns out she's in sickbay, having never left after her initial exam in the first place.
Played straighter in the episode "Frame of Mind" of Star Trek: The Next Generation, where something like this happens... well it's safe to say the episode was about Riker. Maybe.
Also in the TNG episode "Remember Me", everyone on the ship begins to vanish, with Doctor Crusher the only one who remembers their existence. Once she's the only person left on the ship, the rest of the universe begins to disappear as well, to the point where, when she asks the computer the nature of the universe, it has an answer, and specifically that the universe is only the size of the ship.
Crusher: If there's nothing wrong with me, maybe there's something wrong with the universe.
A particularly creepy episode of Stargate SG-1 (3x04 "Legacy") has Daniel Jackson slowly going insane from delusions and terrifying hallucinations caused by a piece of Applied Phlebotinum. Much of the episode is seen from his perspective, resulting in this trope. At the halfway point, however, it turns into a Cuckoos Nest trope when the other characters find proof that Daniel was never actually insane as such. The episode would have been more effective if we, the audience, hadn't been shown some thing infecting Daniel's body right in the first act of the episode.
A Stargate Atlantis episode (3x06) had Weir wake up in an asylum and be told that she had hallucinated the entirety of her time on Atlantis as a way of coping with her fiance's death. The doctors urge her to let go of her delusions to become sane again. In reality she has been infected with replicator nanites that are causing her to hallucinate the asylum.
One of The X-Files episodes ("Field Trip") has Mulder and Scully trapped underground in a giant fungus mycelium, hallucinating that they were trying to solve a case (the case that brought them into the forest, in fact), while in reality the mycelium was secreting a hallucinogenic narcotic compound onto their skin to keep them passive while it slowly digested them.
To further fit this trope, both Mulder and Scully seem to have had the exact same "plot" to their hallucinations, which is pointed out as impossible in the actual episode.
The Criminal Minds episode "Normal". A man takes out his fantasies of killing his family by killing other people. This leads up to a climactic chase scene where he's trying to get his family out of the city when his wife jerks the wheel and makes them crash. When he's pulled from the rubble, it's revealed he had been hallucinating them the whole episode and killed them pretty early on, which is hinted at constantly, in retrospect. It's one of those things you've got to watch twice.
The episode "With Friends Like These" has a young man being pressured by his "friends" into killing innocent people, and they won't leave him alone until he does it. Then it's revealed that he was alone the whole time.
The Lonely Island song/SNL Digital Short "Like a Boss". The "boss" is clearly unstable, and it's possible the hallucinations start after he fails suicide, but after he blacks out in the sewer, it falls into Talkative Loon territory.
Buffy the Vampire Slayer Season 6: A demon stabs Buffy with a weapon that it is a part of it. Said weapon is also poisonous and causes vivid hallucination. Buffy believes she is in an asylum being treated for her delusion that she is the Slayer. After 6 years of watching the show, we the Audience automatically assume that the Sunnydale scenes are real and the asylum scenes are delusion until the final reveal, which has one final "hallucination" that she's gone catatonic.
In the House episode "No Reason", House is shot and is placed into a drug-induced coma. When he wakes up, his debilitating limp is cured, but he soon starts experiencing short-term memory loss and hallucinations while working on a particularly bizarre and seemingly unsolvable case. The other doctors suspect he's suffering side-effects from the drug they put him on, but he becomes convinced that he's actually still comatose. He resolves to break out of his coma by killing his own patient. It turns out that he's right and it works, but there's a moment there where it looks like he was wrong and he's just murdered a man in a particularly gruesome way.
The episodes where he hallucinates of Amber's and Kutner's ghosts count as well.
In Community episode Beginner Pottery Jeff can't accept the fact he is unable to succeed in a pottery class, and ends us stalking and assaulting one of his fellow classmates.
In the Babylon 5 episode "Passing Through Gethsemane", Brother Edward seems to be falling victim to this. At one point, Brother Edward walks through a station corridor. He hears voices, sees a message written in blood on the wall ("DEATH WALKS AMONG YOU"), and "flashes back" to an unfamiliar memory where he's running through water from someone. When he brings station security to the same corridor, as fits this trope, the bloody message is gone. This ends up being a subversion; further investigation reveals there are hidden speakers all through the corridor, there are traces of a "disappearing ink" substance that was likely used to write the bloody message, and the "flashback" was triggered by a Centauri telepath that Brother Edward had encountered just before entering the corridor.
Pete in "Around the Bend", who is exposed to a telegraph that makes him hallucinate a scenario in which Valda has gone power mad and is trying to take over the Warehouse.
Played with in "An Evil Within", where the artifact is a key that belonged to H.P. Lovecraft, which makes whoever touches it be viewed by others as an Eldritch Abomination.
"The Ones You Love" reveals that this has been happening to Artie ever since he used the astrolabe; all his interactions with Brother Adrian since then have been manifestations of his Enemy Within as it grows strong enough to perform a Split Personality Takeover.
One episode of Mystery Science Theater 3000 has Pearl test LSD on Servo and Crowe and hook them up so everyone can see what they're seeing. When they look at Servo's POV, everything turns all nightmarish with Mike and Servo looking more monstrous. Mike is horrified, while Servo just laughs it off and explains that that's what he always sees.
In the Millennium episode "The Thin White Line", the audience sees through the eyes of a young Serial Killer who hears his victims giving explicit permission for him to kill them. His former cellmate talks about people begging to be murdered, but in his case it's ambiguous whether he's speaking literally or metaphorically.
This provides the twist ending for the Masters Of Horror episode "Imprint". After all the horrible events that the disfigured prostitute tells Christopher and the revelation of a siamese Evil Twin, he shoots the prostitute and it turns out to be Komomo all along—the Hooker with a Heart of Gold he was trying to find. Christopher was actually driven completely insane from what's implied to be guilt for raping and killing his sister and the entire story was part of his hallucinations.
As the title suggests, the Coheed and Cambria album "Good Apollo, I'm Burning Star IV, vol. 1: From Fear, Through the Eyes of Madness" contains a lot of this. Maybe.
In a nutshell, The Writer has been writing the story contained within the first two albums. His girlfriend, who he was going to propose to, cheats on him, because he's been spending too much time on the story, and not enough with her. He's angry, contemplates killing her or the character based on her in the story, and starts imagining his run-down old ten-speed bicycle is talking to him, operating as his "Son of Sam" dog of sorts. He ends up Breaking the Fourth Wall of his story, communicating with his protagonist, Claudio Kilgannon...
Coldplay of all bands, did this in "A Rush of Blood to the Head".
The Killers have their "Murder Trilogy." While the "Jenny Was A Friend Of Mine" and "Leave the Bourbon on the Shelf" don't qualify, "Midnight Show" fits pretty well.
The crashing tide can't hide a guilty girl With jealous hearts that start with gloss and curls. I took my baby's breath beneath the chandelier Of stars and atmosphere And watched her disappear Into the midnight show.
The music video of "Asylum" by Disturbed has the patient/protagonist attempts throughout to escape from the eponymous asylum depicted this way. The events within are always surreal and usually overly violent and brutal (such as his being killed or beaten by the doctors and staff multiple times) while deranged and schizophrenic camera editing always follow the patient's POV (scenes without him are completely clean). The kicker is that after every one of his "deaths", he ends up back in his padded cell, implying it was a delusion.During the last event, thinking he'll just be sent back to his cell to tosses himself into a furnace to escape the doctors pursuing him. This one wasn't a delusion.
The Violent Femmes' Country Death Song is sung from the point of view of a man slowly losing his mind, culminating in pushing his daughter into a bottomless pit, and eventually hanging himself.
In mothy's Moonlit bear, Eve Moonlit, played by Hatsune Miku, found two apples deep in the wood and got chased by a bear. As it turned out, the apples are two infants and the bear their mother, whom Eve ended up killing.
Megurine Luka as Sudou Kayo in mothy's The Tailor Shop on Enbizaka is an Unreliable Narrator in this way. In the song, she tells the story in a way which leads the audience to believe that her lover has been cheating on her with three other women who she ends up killing one after another. While her behavior alone makes her out to be pretty crazy, at the end of the song, it's revealed that her supposed "lover" doesn't even know her, and the women she killed were his wife, sister, and daughter. When he fails to identify her, she kills him, too.
One could argue that the events described in The Lonely Island's Like a Boss are a product of Andy's delusions after being rejected by Debra. In fact the entire performance review could be an interview with his psychiatrist.
"What's He Building In There?" by Tom Waits uses this trope in a non-supernatural sense. While nothing supernatural is implied, it's never revealed whether the narrator of the song is psychotically paranoid and obsessively fixating on an innocent (albeit eccentric and reclusive) neighbor as he harmlessly works in his shed, or whether the neighbor actually is up to something sinister in the shed and only the narrator is aware of it.
Candorville generally implies either "everything supernatural is real" or "everything supernatural is a hallucination", but it keeps going back and forth on which it's implying. Saxon's crazy—he thinks he's a Dhampyr. No, wait, he just showed off his Game Face. No, only Lemont saw it, and Lemont sees bizarre things all the time that nobody else ever sees, so perhaps . . . Wait, Susan saw something too! But no, she was only dreaming. It seems the final conclusion will be it's real—Lemont's lawyer is shackled to a wall next to the skeleton of one of his friends, and his captor quite clearly has fangs.
This is the main premise behind Evil Hat Productions' RPG Don't Rest Your Head, where a low-level madness induced by chronic severe insomnia allows the characters to enter a Neverwhere / Dark City style Dark World. Depending on the GM, the setting can be treated as fully real, as existing only in the players' sleep-deprivation-addled heads, or as some combination of the two.
Similarly, there's JAGS Wonderland. So you've started hallucinating and hearing voices — perhaps you're schizophrenic. No, wait, you're not schizophrenic — you've got this disease called Cyclic Psychoaffective Disorder. None of the medical professionals like to talk about it, because you can physically interact with the hallucinations... and it's contagious. No, wait, those aren't hallucinations — they're the things that operate on the lower levels of reality. You're not losing your grip on reality; reality is losing its grip on you.
In the Old World of Darkness Malkavian vampires are all like this. They definitely are vampires and they really do have a piece of a mad undead god in their minds, but other than that they shouldn't completely trust anything they see or hear.
Shakespeare's Hamlet is perfect for this as the entire play is driven by Hamlet seeing a ghost of his dead father telling Hamlet that his uncle, the king's brother, is a murderer. The play then goes on to make Hamlet seem as insane as possible while still keeping everything the ghost said plausible, yet never confirmed.
The guards see the ghost before Hamlet does, although it never speaks to them and never confirms its existence to anyone but Hamlet. Hamlet, at the urging of Horatio (essentially the sanest person in the play), goes out to meet the ghost alone, and only then does it speak. Indeed, later in the play the ghost appears to Hamlet while his mother is with him and only Hamlet can see the ghost. The only person in the play who has solid evidence that there is a ghost is Hamlet, and he very well could be mad as a hatter.
It probably doesn't help that the oldest version we have of the story is from a time where, really, it was perfectly acceptable to believe in ghosts, and Hamlet (or, rather, the character Hamlet is an Expy of) was a fine cocktail of Obfuscating Mental Illness and Badass in a Viking shell, who survives his Roaring Rampage of Revenge.
And of course, whether Hamlet really is mad and/or is just "putting an antic disposition on" has been the subject of massive debate for a couple hundred years. A convincing textual argument can really be made for either, or both. His supposed madness is even lampshaded. Hamlet wonders if the ghost he saw was a hallucination, or a demon sent to him to trick him. He tests this theory out by attempting to make his uncle feel guilty for the murder the ghost described to him. How does he do it? He talks some actors, who are hired to put on a play for the royalty, to modify the murder scene so that it more closely resembled his father's supposed death. His uncle tested positive, making it harder for audiences to argue that Hamlet was simply mad.
A better example might be the Scottish play, where Banquo's ghost torments MacBeth. Some directors leave the ghost out of scene, leaving us to wonder whether the ghost exists or he's just going mad. As nobody else can see it when it is there, he probably is anyway (the hallucinatory dagger was probably the first sign). On the other hand, the man definitely does have witches screwing with his life; he can't have hallucinated them, since Banquo saw them too (although it is sometimes suggested that they were only real the first time he saw them, and that the other encounters were madness-induced hallucinations).
Some productions of Wozyeck designed the setting this way.
In Team Fortress 2's "Meet the Pyro", the world is shown through the Pyro's eyes. In real life, he's brutally massacring the BLU team with fire. In his eyes, he's bringing music, sunshine, and joy to a collection of baby-like cherubs.
In-game you can give yourself eyes of madness by wearing the "Pyrovision Goggles"; eyewear that make (supported) maps bright pastel in color, replace shouts of pain with laughing, makes everyone voice's high-pitched, and replaces messages of one player dominating the other with ones saying they're becoming friends.
In The Binding of Isaac, there are many; many hints that the whole of the game is this for Isaac. In fact, according to this analysis, which Edmund McMillen himself called "By far the most mind blowingly accurate break down of the over arching meaning behind the game's ending", the whole central theme of the game is Isaac deciding whether he will stay and die in his own self-created delusion or return to reality.
A lot of the creepiness comes from the fact that there ARE actually monsters, zombies and demons around... but is that sound of earth-shaking footsteps right behind you one of them, or just a sign that your reality-check has finally bounced? When a healing spell misfires and blows off your torso, it could just be because the magic you use comes from an accursed tome of darkness, or it could just be a hallucination... also, the fact that most of the characters you play end up going mad, dying, or both, helps to drive home the point.
Of particular note is Dr. Maximilian Roivas. When playing as him, several of his servants suddenly attack him, and after killing them are revealed to have been possessed by Bonethieves. Listening to the comments of his Bonethief autopsies, as well as a later cutscene, strongly imply that not every servant killed had been the victim of a Bonethief... If Max talks to one of the female servants before he picks up the Tome of Eternal Darkness, she makes (relatively) normal conversation. After picking up the tome and incurring a bit of sanity loss, she giggles and tosses "something that looks like a human organ" into the cooking pot. However, if you kill her, you take a massive loss of Sanity, just as if you had killed someone innocent... and no Bonethief pops out of her.
The Half-Life mod They Hunger played with this in the third chapter. The intro cutscene shows a hospital, with a doctor mentioning a delirious patient who keeps screaming about the living dead, as a baby from the maternity ward cries in the background. Then the game starts, and you jump out of your hospital bed and start killing the zombies who have taken over the hospital. But as you fight through the city, you keep hearing a baby crying...
Oracle Of Tao has Ambrosia, a girl supposedly called by God to save the world. The problem is... it's unclear to her whether or not her quest is even real, much less her traveling companions. A possible interpretation of what's going on is that aside from meeting her party, the entire quest is a giant delusion of a girl hoping to feel important because her birth parents abandoned her.
Silent Hill 3 raises the possibility that it's an example of the trope, with a character first angrily decrying ("You come here and enjoy spilling their blood and listening to them cry out! You feel excited when you step on them, snuffing out their lives!"), then shockedly asking the game's protagonist, regarding the creatures she's fought and killed for the whole game, "Monsters? They looked like monsters to you?" He claims to have just been kidding... but he may have been just saying that to calm her down and the monsters were just her mysticism-addled visions of innocent bystanders... but then again, maybe he really was just kidding.
The whole "the monsters are actually people" theory was brought up previously in Silent Hill 2, and later in Silent Hill Origins. In the former, returning to the area where James killed his first monster will find it blocked off by police tape, raising the question of just what exactly James bludgeoned to death with a wooden plank. The Bad Ending of Silent Hill Origins shows a drugged and restrained Travis strapped to a table, apparently suffering a psychotic episode, with snatches of dialogue playing that strongly indicate that The Butcher was actually Travis himself, and that Travis was just going around slaughtering innocent people for the whole game. Since the Good Ending leads directly into Silent Hill 1, however, the Bad Ending is probably not canon.
Silent Hill 2. It's all in your head James. But if that's true, then why is it that "You see it too? For me, it's always like this."
Presumably, James has entered Angela's 'Otherworld' when he sees the flames, just as he entered Eddie's when James fights him in the meat locker. Also, another case of this trope is the Abstract Daddy: a monster to us, but to Angela, it looks like her father. And for that matter, nobody ever sees Maria except James...
Silent Hill: Shattered Memories may be a game about Harry trying to find his daughter Cheryl. Or maybe it's about Cheryl finally giving up on her delusions of her father's ghost. But how does that explain Harry's conversations with Cybil? Or Michelle? Or Dahlia? Or any of the people he spoke to over the phone?
It doesn't explain it. In fact if you call the mall security, they mention that Harry can't be where he is, otherwise he would have tripped the alarms or shown up on the security cameras. Harry can't explain it either. This basically says that Cheryl's subconscious did create something. Maybe.
Call Of Cthulhu: Dark Corners Of The Earth, a game that comes complete with Sanity meter and hallucinations, is based on the works of H.P. Lovecraft. Thus, while it's easy to believe the events chronicled are real, the beginning (which is also the ending, where the main character hangs himself in an insane asylum) coupled with repeated hallucinations of still being in the asylum during the game cause one to wonder if he is mad because of the events or the events came from his madness.
Certain missions in Max Payne are examples of this, as is the show-within-the-game Address Unknown.
The Darkseed duology, particlarly Darkseed 2. The main character is undergoing therapy, and the psychiatrist just doesn't believe that the Dark World really exists. Given the ending, whether Dark World exists really or is just a hallucination of Michael Dawson is an open question.
Postal casts the player as a stressed employee turned paranoid delusional who goes on a horrific rampage. And why does he do this, you may ask? While it's probably all about revenge subconsciously, he's deluded himself into believing that the town he lives in must be terminated because it's inhabitants are insane. Talk about projection.
Postal 2: Apocalypse Weekend plays with this trope. The game takes place after the Postal Dude has suffered a gunshot wound to the head at the end of Postal 2, and as a result he often finds himself transported to a Silent Hill-like "alternate reality" version of his current location, where the walls are made of blood and Gary Coleman-like demons appear and attack him. It's probably just a head-trauma-induced hallucination, though. Probably. Postal Dude even remarks "With my luck, that's really a nun. Or someone's grandmother." after blowing away one of the demons with his firearms; being the guy he is, though, he follows this up with "but there's no sense in taking chances".
The alternate ending to Scratches: Director's Cut has elements of this.
Baldur's Gatenearly goes here. You're told, late in the game, that your foster-father, Gorion, was actually poisoned, not killed, and that the doppelgangers you've just been massacring really were the childhood friends they at first appeared to be. Then the characters who told you this — Elminster, Gorion and Tethoril — turn out to be disguised doppelgangers, not themselves.
The manual to American McGee's Alice has the case notes of Alice's psychiatrist, which match the action in Wonderland very nicely. Is Wonderland some sort of objectively real dimension Alice is traveling in? Is it nothing but Alice's insanity? Is it somewhere in between and that nasty "psychiatrist" is helping crack poor Alice? You're never really sure, especially since the opening cinematic implied that the denizens of Wonderland woke Alice to save her life during a house fire.
Taken Up to Eleven in the sequel, when we actually see Alice blending Wonderland and the real world. Maybe. It's not very clear... It's even been suggested that she was lobotomized halfway through the game and it was All Just a Dream.
Sorry to dissapoint: Word Of God says it's for real. She regained her health, she pulled her confidence from the depths of her mind to the real world, and now, everybody in this Crapsack World will see Through the Eyes of HER Madness.
Sanitarium. The Reveal is sprung too early, but until then, it's not clear which parts are real, which parts are the main character's demented hallucinations and which parts may be someone else's deranged hallucinations.
This trope is the main source of horror in Phantasmagoria 2: A Puzzle of Flesh. The main character was recently released from a mental institution, and throughout the game sees and hears horrific things that no one else seems to notice.
The Suffering is very much built around this trope. On the one hand, there's definitely monsters tearin' shit up. On the other hand, the main character, Torque, is definitely out of his damn mind. On top of the constant hallucinations, he can transform into a hideous monster that does excellent melee damage to foes, but suffers from health damage if used for too long. It's eventually revealed that Torque only imagines his transformation and the weird attacks he uses while in the form of the monster: it's all just him slaughtering people with his bare hands. This becomes very obvious when other characters react with surprise at how many enemies Torque killed while transformed, but never seem to notice any physical change.
Bioshock 2. At the particular moment of the game, you got to see the world through the eyes of a Little Sister for a while, which is true cognitive dissonance.
In Batman: Arkham Asylum, you progress through multiple surreal segments in which Batman is exposed to the Scarecrow's fear gas, and he is forced to witness his worst fears becoming real and to re-live the most horrifying and psychologically scarring moments of his life.
The sequel, Batman: Arkham City, also has a segment where Batman is given the "Blood of the Demon" from Ra's Al Ghul and hallucinates surreal terrain and phantasmal enemies. In another he must shrug off the Mad Hatter's mind control in a battle that looks (to him) like it's taking place on the face of a giant watch floating in a bizarre environment. Batman also spends a good chunk of the game slowly dying from blood poisoning and at one point is fighting Mr. Freeze and sees his face turn into that of the Joker.
Some encounters with the Lovecraftian Old Gods in World of Warcraft including unsettling whispers directly to the player. A both very creepy and amusingly literal take on the "in the mouth of madness" phrase occurs if you die in the "brain" area of the fight with Yogg-Saron: your body appears in the middle of the boss itself, with your camera gazing out through its immense, gnashing teeth.
In the Dead Space universe, there's quite a bit of this due to the influence of the mysterious Markers.
In Dead Space, Isaac goes aboard the Ishimura to find his girlfriend who has been dead this entire time, and it was a combination of guilt, denial, and the Marker that made him believe she's still alive. The Mole reveals the truth to him before she's crushed into paste by the Hive Mind.
In Dead Space 2Isaac is fully aware that his mind can't be trusted and that Nicole is a hallucination, but he eventually begins to trust it which makes the vision's betrayal all the more awful at the end. Also, Stross is in the throes of this throughout the game.
In Dead Space: Extractionthe first chapter is pretty much this, Sam Caldwell believes that dozens of maniacs are attacking him all the while being assaulted by mysterious symbols and the voices of his dead friends, but it turns out that he's just been shooting innocent people this entire time. He comes to this realization after being gunned down by the police.
In Dead Space 3, Isaac has dealt with his personal demons since the last game, so he doesn't have many psychotic episodes. But the slack is picked up by the second protagonist, John Carver, in Co-op mode. Meanwhile the Awakened epilogue DLC is just about half hallucinated by both characters, with a fair chunk of the enemies not even, technically, existing.
Alan Wake toys with this a few times, but ultimately, things reach the point where an actual malevolent supernatural force is the only reasonable explanation.
Catherine: Catherine herself exists only to Vincent and the other men she is seducing (as versions of their ideal sex-pot); she's a succubus. This causes Vincent some grief towards the end of the game.
Spec Ops: The Line uses this to deconstruct the military-shooter genre. The protagonist is eventually overwhelmed by the horrors of Dubai; after this point, he starts imagining things, and the player isn't privy to what's real and what's in his head. At least twice, the game blatantly telegraphs that this is going on, but the clues leave out just how far gone he is until the ending. Really, reallyfar.
In the Overlord DLC for Mass Effect 2, Shepard has their cybernetic implants briefly hacked by a rogue AI, causing them to see the entire world in Matrix Raining Code, as well as video feed depicting an autistic man named David Archer who can communicate with the Geth. It turns out that David Archer is the rogue AI, having driven half-mad after being hooked into computer mainframe by his amoral brother and he was causing things to go haywire whilst trying to scream for help!
Vampire: The Masquerade – Bloodlines is one of the few RPGs that lets you play an actually batshit insane character—a vampire of the Malkavian clan. Pretty much all dialogue in the game plays differently as a Malkavian than as other clans, and among other lovely perks, you can have thoughtful discussions with TV sets and road signs, and realize in unholy terror that the cabbie that has been driving you around LA is actually Caine the Original Freaking Vampire! Or is he?
Masterfully done in Tatarigoroshi-hen. In order to protect Satoko, Keiichi kills her Evil Uncle. But the next day, Satoko insists that her uncle abused her later that night and his other friends say Keiichi was at the festival at the time. But wait! The uncle's missing and the body isn't where Keiichi buried it. Satoko still insists that her uncle is abusing her. Keiichi did kill Teppei and everyone's providing a cover story. Why does Satoko insist Teppei is still alive? Well... Just because Keiichi is the Unreliable POV Character doesn't mean he's the only one going crazy, does it?
In Umineko: When They Cry, no witnesses survive the murders, but the audience is shown the spectacularly magic action sequences. In this case, the "madness" is actually invoked; the idea is that the Game Master claims that all the murders are done by magic, and the object of the game is to break "the illusion of the witch" and figure out how they could have been done by human hands.
Saya no Uta... Through the eyes of Fuminori, whose senses had been inversed, every human being is as disgusting as a pile of organs and putrid flesh pouring pus. Not only do humans look this way to him, but every single shape (His house, the sky, the cars) looks like it's covered in guts and gore. Everything smells foul, sounds foul and feels foul to him. The actual Eldritch Abomination looks like an angel to him. And then he finds some meat that smells nice...
Chaos;Head features a main character who is a self-described disgusting, delusional, otaku, hikikomori who is approached by several beautiful girls all with a mysterious connection to a series of murders going on in Shibuya. This makes it extremely hard to tell where the events of the series lie on the line between paranoid hallucination and supernatural strangeness — if there is in fact any separation between the two at all.
As it turns out, the main character himself is the equivalent of someone's Imaginary Friend taking a life of his own and turning into a Not-So-Imaginary Friend. The "real" Takumi is a wheelchair bound old man with a terminal illness. The teenaged, otaku Takumi is the result of the "original" Takumi's near Reality Warper level ability to project "illusions". The delusions that Takumi experiences are likely linked to his nature as a Tomato in the Mirror, and not because he's suffering from a lack of sanity.
Under the influence of blue mushrooms, the cast of College Roomies from Hell!!!!!! have hallucinated multiple times, yet there's hints of truth slipping through the haze. In the most recent case, they fully realized they were hallucinating and went with it anyway just in case they learned something important.
Several well-known Creepypastas, such as "Grocery List", employ this trope. The Creepypasta Wiki also has a category labelled "Mental Illness".
Linkara described ''Marville as "a gaze into the eyes of madness" to how it's author Bill Jemas thinks the world works.
Sky Does Minecraft is the only member of Team Crafted who can actually understand squids. Can make the mod showcases in which a squid has the spotlight fall under Mind Screw.
In an American Dad! episode promptly called "The American Dad After School Special", Steve revealing that his new girlfriend is chubby makes Stan horribly self-conscious about his own weight and begins excessively dieting, with help from an enthusiastic coach named Zach. However, despite Stan's best efforts he keeps gaining weight, and it appears as though his family is sabotaging his diet so as to make him feel bad and apologize to Steve. However, after being sent home from work after passing out during a physical, the family confronts him about his weight issue and state that he is really anorexic. At that point, it's revealed Stan wasn't getting fatter, he was suffering from a delusional state of mind and lost so much weight he was practically a walking skeleton. His personal trainer also turned out to be a hallucination, and Francine and Hayley's "sabotage" was really an attempt to make Stan better.
"100 A.D." has Roger being high on Turkish amphetamines, hallucinating that he's driving on a weird planet with Steve as a Nazi walrus and Klaus as Garfield.
In the Ed, Edd n EddyHalloween Episode, Ed watches so many B-grade monster movies that he starts hallucinating and seeing everyone that he meets as monsters, such as the Kankers as witches and Kevin as the Headless Horseman. At the end of the episode he then sees Eddy and Double D frolicking in flowers when in reality the kids are beating them up.
In the My Life as a Teenage Robot episode "Daydream Believer", Jenny is given a chip to allow her to simulate dreaming. When she tries to activate it during the day it breaks, causing reality in her eyes to resemble the world of Dr. Seuss crossed with Roman mythology.
Her "party guests" in "Party Of One". They're a bucket of turnips, a pile of rocks, a sack of flour, and a pile of lint. She gives them names and voices, and moves them around to simulate them "talking". Once they "ask" her the Armor-Piercing Question, she loses any sanity she had left and the "party guests" start moving and speaking on their own. Then, the camera zooms out, and the "party guests" are just as inanimate as they always were...
A very mild example occurs in the Adventure Time episode "Red Starved". Finn is looking for something red for Marceline to feed off and finds a large ruby, but a monster Finn talks to keeps insisting it's an emerald. Once Finn brings it up to Jake and Marceline, it turns out it actually is an emerald (the shown color changes from red to green), and Finn is color-blind.