You'd think that it all being just a dream would let you do lots of cool and risky things since it's not real anyway, and therefore you can't get hurt.
There's an old wives' tale which claims that if you die in a dream, you die for real. Although a potential mechanism is suggested in "Real Life" below, it remains not exactly clear how anyone could have determined this, since the only witness would be unable to confirm it. Yet it persists, and a lot of people believe it.
So, if you're in a dream, hallucination, or VR simulation, death can be plenty lethal. By extension, if you're a hacker in a high-tech futuristic world where Cyberspace is navigated through a realistic simulation, intrusion countermeasures can kill you dead. To be fair, certain depictions of Cyberspace require users to electronically link their brains to the network, which would provide a relatively obvious threat to incautious intruders. However, even hackers who operate in worlds without such dangers may be vulnerable to seizure-inducing graphics.
Often, fictional cyberspace ICE (intruder countermeasure electronics) is said to work by channeling lethal voltages into the brain of the invading hacker, but it seems that any techhead with even an ounce of common sense would put at least one fuse, circuit breaker or voltage regulator, on any line connected directly to his brain. Presumably most users do not know about such things, given their willingness to use an interface that could turn them into a vegetable or corpse at a moment's notice. Authors who put a little more thought into the matter may come up with some variant of the motif of harmful sensation, implying there's some kind of malicious out-of-band signal which triggers a nasty (usually fatal) seizure in its victims or blows up their computer.
As for the rest? Let us be very clear: there is no obvious or immediately compelling reason that dying in a dream or hallucination would actually kill you, unless you are really gullible and you live in a world where the placebo effect is much more powerful than it is in real life. Obviously, magic spells can do as they like, but the only reason that you would be actually harmed by dying in a VR simulation would be if the VR simulator was intentionally and specifically designed to murder the operator. This makes sense if it's part of a Death Trap (insofar as a death trap ever makes sense), but usually this is some commercial, publicly available system, often with no stated purpose beyond simply ''playing games''.
As an extension, perhaps to justify this trope, such systems often propose that the user's mind actually is inside the machine, having been literally downloaded out of his physical brain. Thus, destroying the machine would leave the user's body comatose — but destroying the physical body might leave the mind intact to have a go at possessing someone else.
An increasingly common justification of this trope is Synchronization; directly wiring your brain to the machine gives you TechnopathicPower at a Price of a potentially fried brain. Most Cyber Punk games — such as Shadowrun — use this justification, and lampshade it with alternative safer but far-less effective interfaces which someone risking a Brain/Computer Interface can destroy with ease.
This tends to apply to video game levels that are All Just a Dream or a virtual reality simulation as a function of gameplay: If your character dies, it's still a Game Over.
When you are Talking in Your Dreams with someone else and they go to kill you — this may come into play. This may also come into play if, in a dream, a character dies, and that character dies in real life, however, this would be an overlap with Clap Your Hands If You Believe and I'm Not Afraid Of You. The Master of Illusion might use this principle to make their illusions harm victims, like making Cold Flames actually burn.
Frequently pops up in a Holodeck Malfunction. See Self-Inflicted Hell. When your mind actually changes the physical world, it's Clap Your Hands If You Believe, or the much darker Reality Warping Is Not a Toy. Forget telling yourself not to think about the things you see - for it will become real here. If a computer generated or magical illusion changes the physical world, it's Hard Light. When you're trapped in a virtual world, and have to win or die, its Win to Exit. For instances where getting killed in a dream actually can kill you for real, see Never Sleep Again. Compare Puff of Logic, Magic Feather.
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The final battle in Tengen Toppa Gurren Lagann takes place in something called Super Spiral Space, the space outside the galaxies, where "recognition is given real form". In other words, whatever they imagine exists, exists. Ergo: Your mind makes it real.
Subverted in Scrapped Princess, when the titular character enters a VR program to save her brother from being brainwashed, only to be promptly impaled by him when he fails to recognize her. There is a moment of shock, and then she slaps him in the face and continues to shout at him with his sword still stuck through her.
Get Backers is fond of this trope, and used it in the IL and Divine Design arcs.
In the .hack series, characters hit by the Data Drain attack within The World are usually sent into a coma in the real world, and are temporarily knocked unconscious at the very least.
Some characters eventually realize that somehow their minds are taken inside the game world, experiencing it with their character's own senses instead of being at home with a headset and game pad. Naturally, they become deeply concerned about what's going on with their physical bodies, and what happens if their characters are "killed" in this state.
There's a bit of question in regards to whether the player stuck in the game and the coma victim are related in that manner. Word of God has dropped that the original coma victims were placed in a coma due to noise affecting their mental state, placing their reliance of the physical body explainable only under the conceit that Everything Is Online. In the latter anime and game series, ROOTS and G.U., the danger is a viral Wetware Body existence that uses Harald's original human observation algorithms to affect the mind directly.
Early in Rurouni Kenshin, during the final battle between Kenshin and Jin-e, the latter reveals that his technique Shin-no-Ippou works based on this principle: he projects a mental suggestion to his victim(s) physical body, which usually causes people to get frozen in place, but can be used in other parts of the body; he nearly asphyxiates Kaoru by paralyzing her diaphragm, and she managed to break out of it from her fear that Kenshin would kill Jin-e and become Battousai again. In short, enough willpower on the target's part renders the technique void.
Digimon Adventure: Towards the end of the second Story Arc, Local Boy Genius Izzy figures out the Digital World is a world made out of the data of the world's network infrastructure and hence all the human protagonists are more than likely made of data in that world. Although he tells everyone to be careful in spite of this new development it doesn't sink in with Tai, the goggle boy leader of the group, and he starts acting like a jackass under the flawed logic that he'll somehow survive regardless of what happens. It takes Izzy telling him that he would more than likely die in both worlds if he messed up to put a stop to his nonsense. Unfortunately, this happens just after a member of the team is kidnapped and they're about to cross an electrified gate to go after her. He loses his bravado right there and the kidnapper gets away more or less scott-free, leading to a short term Heroic BSOD for Tai.
Digimon Tamers: Henry and Takato manages to cross a massive expanse of water without drowning by convincing themselves that they would only drown if they thought they would.
Digimon Frontier: Played with when Sixth Ranger Kouichi's consciousness was pulled into the Digital World by the would-be Big Bad Cherubimon. Because of this, he's technically not there, he only believes he's there. It begins to dawn on him that this might be the case when survives several curb stomp battles virtually unscathed while his friends get more and more roughed up. Although at the end, this turns out to be an even more convoluted usage when all of the hinting about the aforementioned results in Kouichi realizing that he is actually dead in real life; he thus makes a Heroic Sacrifice to combine his power with Kouji's to defeat Lucemon, under the justification that out of all of them, he's not really alive in the first place. The Power of Friendship saves him, in the end; this isDigimon, after all.
Apparently how Hunter × Hunter's Greed Island arc works, up until the eminently satisfying reveal that the virtual reality game can have such far-reaching real-world effects because it is taking place in the real world.
In JoJo's Bizarre Adventure, this is the power of the Stand "Death 13": it pulls its victims into a dream of an amusement park and then kills them while they're trying to figure it out.
In a later example in the same series, the trope is used to make people believe that they are snails due to subliminal messaging. Yeah, didn't make all that much sense in context either.
In Sword Art Online, Virtual MMOs have pain inhibitors that prevent this from happening: if a player's pain inhibitor is turned down low or completely disabled, they can suffer actual bodily harm in the real world. However, the players will die for real if they die in the game (the helmet used to play the game will unleash a pulse of microwave radiation that will kill them).
Half of the Story Arcs in Yu-Gi-Oh! are about soul-sucking Virtual Reality games. The other half are about soul-sucking millennium items.
Happens in Mahou Sensei Negima!, during Negi's test to learn Black Magic. He has to fight a phantasmic version of Evangeline formed from his memories inside his head; meanwhile Chisame has to take care of him, as wounds start appearing on his body as a result of the test, and a lot of Blood from the Mouth.
In Fushigi Yuugi, Tomo of the Seiryuu Seishi is the second-strongest of the group because his illusions are so convincing and complete, they can cause physical damage, even to people who are already aware that his illusions are just that.
In A Certain Magical Index, Útgarđa-Loki is a Master of Illusion, fitting for a mage based on the mythological giant illusionist. He's so good at this that he can make someone feel like he is on fire by showing him a picture of a fire.
This trope is essentially the fuel for the phenomena in Paranoia Agent. It all boils down to belief. When there is enough belief in something (through numbers and/or intensity), it manifests. Such as with Lil' Slugger/Shounen Bat. More and more people believe in the legend that he comes for people on the brink of the Despair Event Horizon, and he thus appears more and more frequently...and all the victims are smiling afterward because they found release. Eventually, the late episodes show the manifestation of imagination beginning to intensify: Ikari's "ideal world" and Maniwa's half-crazed journey to discover Lil' Slugger's origins (the line blurs here because, despite them seemingly being delusions, he learns real facts).
In Bleach, Rojuro "Rose" Otoribashi's Bankai generates music that causes the listener to experience illusions. These illusions feel solid to the listener and can harm them. However, being deaf makes one immune to the illusions.
For clarification, completely deaf, at the very least. Rose all but said that covering the ears would do nothing, but it apparently requires functioning ear drums.
In the Doc Samson miniseries, Tina Punnett is trapped in a VR game that's been modified to cause psychosomatic damage to the player. To get out, she runs herself through with a sword, causing lots of pain but also causing the game to end.
Uncanny X-Men #133: Cyclops and Mastermind have a sword fight on an "Astral Plane", concluding with Mastermind stabbing Cyclops through the heart. In the real world Cyclops' body slumps over and Nightcrawler loudly announces "Cyclops is Dead!" He got better by the next issue.
Danielle Moonstar, Mirage, has the ability to create illusions based on one's fears. When her powers were temporarily boosted she could make the illusions physical, with the images being more powerful if they scared the person more.
Trauma was a mutant introduced during Avengers: The Initiative who could become one's greatest fear. It's presumed that Trauma only gains power if his opponent fears what he's turned into, since he's been capable of turning into Thor, Hulk, Juggernaut, and several other people/creatures whose power levels are insane. However in a battle against the Hulk during the World War Hulk arc, it was discovered that if his opponents can control themselves during the fight and rein in their fears, he loses power.
One issue of Generation X had the old wives' tale quoted at the start before the team had a slasher movie marathon. The rest of the issue consists of Jubilee in a semi-lucid dream trying to wake up before combinations of movie killers and villains she'd faced in her adventures (ex. Sabretooth with Freddy Krueger's outfit) killed her.
In Star Wars: Legacy, Darth Andeddu conjures illusions of flames and lava and sends them at Darth Wyyrlok. Wyyrlok takes control of them and sends them back. Andeddu is killed, and Wyyrlok muses that Andeddu's own fear made the flames real to him.
In the My Little Pony fic Moonlight, while no one has actually died in the dreams, Scootaloo has experienced how injuries taken during her dream journeys will manifest on her real body as well.
Films — Animation
Paprika has a moments where the dreams and real life can't be told apart because of this trope... Both for the characters and the viewers.
Films — Live-Action
In Brainstorm, a character dies while hooked up to a tape that records thoughts and experiences. Someone else "watches" it, and has the exact same heart attack, dying in the process because they didn't disable the pain generators.
David Cronenberg's The Brood starts off with a doctor whose therapy involves making mentally ill patients make their illness a physical one, which he would then cure, hey presto reverse placebo! The titular brood is the result of a woman who had motherhood or something as part of her many issues...
Dreamscape, which includes a guy entering the president's dream in order to kill him.
This happens in Gamerat the end. "See this knife? Picture me driving it into your stomach. Imagine it and make it real."
The Matrix is the trope namer. Judging from Morpheus's words (which incidentally make up the trope name and quote), this is presumably Hand Waved by the fact that the Matrix simulation overwrites reality for your brain, hence your brain shuts off because it's being force-fed the sensation of death. Whether or not it was purposely designed to do so is never stated, though either way, the Machines sure wouldn't want to change it.
However, in The Matrix Online, safeguards have apparently been put into place that when a redpill is killed in the Matrix, an emergency switch jacks them out of the Matrix, forcing them to re-enter at a hardline after some recovery time.
In the original movie, Neo subverts the trope. After he ascends to full-fledged One status, his control over the Matrix becomes so great that he apparently wills himself to life.
Also averted in the training programs, which are designed to show you that you can die, but without actually killing you. For example, the "jump" scenario is considered impossible for a new red-pill to pass, as they cannot perform Roof Hopping yet. Fortunately, the ground below is made to absorb most of the impact, only causing the trainee a fair amount of pain and wounding them slightly in the real world.
A Nightmare on Elm Street. Freddy Krueger has the power to kill people in their dreams. Any damage that he inflicts on you in a dream crosses over into the waking world.
Both subverted and realized by Inception, where any physical damage in the dream world, even killing yourself, has no physical ramifications in the real world; but mental manipulation within the dream world has mental and thus physical ramifications in the real world.
In Surrogates, originally people could operate remotely-controlled surrogate version of themselves without any risk - no damage done to the surrogate could have any lasting effect on the operator. Naturally, someone finds a way to subvert this rule, and this is when the problems (and the plot) start. This is different from the original graphic novel, where there is no way to kill a person via his or her surrogate.
In Stay Alive, a group of beta testers realize that they are slowly dying off one by one in the exact same fashion that their avatars in the game they are testing die. It is later revealed that playing this game summons the ghost of a sociopathic killer who delights in killing you in the most horrendous ways possible.
Averted in Strange Days, where dying in a virtual reality clip is a popular form of Snuff Film. However, such clips are against Lenny's scruples, and he hates "the zap when they die".
The Thirteenth Floor was sneakier: you enter a virtual world by possessing one of its inhabitants and if killed in this state, your mind dies. And not only that, but the victim's mind takes over your body instead because it turns out the process is actually a complete mind swap. No one realized this because the real body usually remained completely unconscious during the process. Virtual death merely broke the connection and jarred the real world body with the virtual mind inside it awake.
Virtuosity is not a straight example - the system is designed to train cops in combat situations, similar to the US Army's Real Life Force XXI program. The problem is that different people worked on different parts of the system - and didn't understand how Lindenmeyer's maniacal AI could abuse it. The Dev Team Thought of ALMOST Everything - they programmed in non-lethal simulations of being shot, bludgeoned and even bitten - but when Sid decided to try electrocuting someone, the poor chump's brain overloaded.
Sid 6.7: Killing for real... It was a real rush.
The Wheel of Time books include a special dream world that can be accessed through special artifacts, training, or blind luck. Injuries and death carry over. It even explains people dying in their sleep for no apparent cause as them accidentally dreaming themselves temporarily into the dream world long enough for something fatal to happen to them.
In The Hitchhiker's Guide to the Galaxy series' fifth book, Mostly Harmless, Ford enters a virtual world in which some inhabitants carry laser guns. If they shoot you, you're dead, as you're "as dead as you think you are."
In King of the Water Roads the magic of "Seeming," which is based entirely on illusion and bending a person's perception, can be used to murder if whatever illusions are being used are strong or traumatizing enough.
In The Pendragon Adventure, the territory of Veelox has a virtual reality system called Lifelight. It is initially stated that if you die during a Lifelight "jump", you simply wake up from it. However, once the Reality Bug is introduced into Lifelight in an attempt to make it less perfect and addicting, this trope gets taken to absurd levels. Not only do you die in real life if you die during a jump, but any injuries you get appear on your real body, even damaging your clothing. And after the Reality Bug manifests in a jump as a giant shape shifting monster, it is somehow able to enter physical reality by burrowing down through the ground. Bobby even admits that all this violates the laws of physics as he understands them.
In G. A. Effinger's When Gravity Fails, eight people lie down at a Virtual Reality couch, and only seven get up. One of them figured a way to make one of the others fail to go back to their body, causing their "soul" to be purged when the machine shuts down.
In William Gibson's Neuromancer, and other stories set in the same world, console cowboys interact with computing environments through virtual reality on a deep enough level that they risk brain damage or death from tangling with the wrong entities.
In Tek War, failing to hack a computer system results in real injuries ranging from brain damage to death. Fortunately, most hackers can spare the brain cells lost in minor skirmishes.
In Maskerade, the villain is killed in a sword-fight, but it was stage fighting, and the sword is just held under his arm. However, he (and everyone else in the opera house) has been so immersed in drama and fiction for so long that it kills him because he expected it to.
Using "Headology" (directed YMMIR) is a large part of being a witch. Granny Weatherwax makes liberal use of it and promotes its use in her pupils over the use of actual magic.
Susan uses this trope to its maximum effect, developing her wards' belief in a poker she uses to beat up the monsters that hide under the bed, rather than telling them these monsters don't exist. That is, while she realizes nothing will make them stop believing in monsters, it's much easier to make them believe she's enough of a badass to take them.
In Hyperion, a cyberspace hacker's head explodes when he is exposed to a section of cyberspace inhabited by AIs, which is normally inaccessible to humans. In this case, it's a completely real security system which causes his implants to boil his brain. When people are Mind Wiped during a network crash, however, that's the trope played straight.
Russian cyberpunk literary classic Labyrinth of Reflections by Sergey Lukyanenko used a massive VR world... based on Doom. Considering the state of the nigh-post-Soviet information network in 1991, that makes some sense.... The trick was a hypnosis program of sorts known as Deep that put the user in a trance-like state; the relatively limited visuals they were given were filled in by the brain's natural ability to add extra data (akin to limited side effects of sensory deprivation) and an immersive world was created. The trick was a very small, professional group of "Divers" who could bring themselves out of the trance-state at will, and interface with the system as it actually existed. Also there has been made a certain virus in the Deep that actually kills the users. And one that traps divers.
In the third Hellgate: London novel, a demon used a device which made the target relive his/her past in the dream, which will go horribly wrong and kill them, or make them go crazy.
In the Memory, Sorrow, and Thorn series, by Tad Williams, the Dream Road is a metaphysical realm that is touched on by all thinking beings while they sleep, but that practitioners of the Art can enter intentionally, bringing others with them. Things that happen to one's mind on the Dream Road can and do affect one in reality, and in the most benign of circumstances it's possible for an inexperienced traveler to become "lost" and unable to return, leaving their body an Empty Shell. In less benign circumstances, there are ... things there that can actively destroy all but the most powerful minds. Such encounters are typically fatal (orworse) to the dreamer.
One of the central mysteries in the Otherland series, by Tad Williams, is why this trope seems to be occurring. Brown Note effects are known to exist, but they require especially high-quality virtual reality interfaces, and yet the Otherland network somehow manages to deliver sensations that the users' equipment is incapable of generating, and keeping them trapped online even when they ought to be able to simply remove their VR gear. The answer is that the operating system has Psychic Powers.
In The Saint short story "The Darker Drink", Simon Templar encounters in the High Sierras a man named "Big Bill" Holbrook who claims to represent the dream avatar of Andrew Faulks of Glendale, California. Holbrook notes that Faulks had started to have an increasingly vivid recurring dream, such that smell and tactile sensation emerged. It appears that the personages in Faulk's dream (such as a woman named Dawn Winter) had started to manifest in the waking world. Templar notices curious phenomenon which seem to support Holbrook's claim: Simon sees his own reflection fine in a small mirror, but Dawn's features are "blurred, run together, an amorphous mass"; when every single character repeats the same cluster of honorific catch phrases when they first meet the Saint; and the phenomenon of time compression that Holbrook identifies as an aspect of dream (a group of thugs searching for Holbrook and Winter say they will travel a long distance to fetch their boss from the town return in less than thirty minutes). Though one of the thugs opens fire on Templar, he has no wounds in the morning. However, when he visits Glendale, California to look up Andrew Faulks, Faulks has died after slipping into a coma.
One of Dumbledore's famous quotes from Harry Potter and the Deathly Hallows seems to address this trope. "Of course it is happening inside your head, Harry, but why on earth should that mean that it is not real?"
In a nutshell, what O'Brien explains to Winston at the end of 1984: that as long as the people believe it happened and there is no written evidence to the contrary, it actually happened, and screw the laws of nature if BB says so. In fact, the ideal citizen is one who can subconsciously alter his perception, memory, and experiences to meet whatever the Party says in order to make it true. Of course, the mind doesn't change any independent physical things, but that's not the point, since the Party doesn't really believe in those anyway, or at least doesn't care about them. Basically, they're saying that this trope applies even though it doesn't apply.
Magicnet falls somewhere between this and Clap Your Hands If You Believe, depending on whether you view magic as a shared hallucination, or the product of an alternate reality that coexists with this one. Characters who truly believe that magic exists can and do get hurt by it, but a large amount of what occurs is shown to be just smoke and mirrors once characters deny it (e.g. a supposedly exploding plane engine turns out to be undamaged.)
In a case of "Someone Else's Mind Makes It Real", in Anne McCaffrey's The Rowan, it was first thought that Prime level talents suffered from debilitating vertigo (known as Travel Sickness) if they attempted interplanetary travel. Then along comes Jeff Raven, an untrained Prime from a frontier colony who could bounce around with no ill effects. It was later discovered that the only one of the six known Primes that did have that condition was Siglen, who had an inner ear condition that really did cause her to fall ill. Siglen's giant ego subscribed this to "the burden Primes must bear for their power," rather than have herself checked out. Since Siglen trained or trained with all the rest of the Primes, she mentally pushed her condition on the rest. The Rowan was the only one of the original five young enough to train herself past her conditioning. And then, preferred staying on her home base of Io, Jupiter's moon, unless she had to travel.
In Epic by Conor Kostick, toward the end, the bad guy is in Epic, and a vampire rips his character's heart out. His heart stops in real life as well. The "vampire" was actually an avatar of the game itself, as it has gained sentience, so that may have had something to do with it, but nowhere else in the trilogy do any games physically affect someone.
Thoughtforms in Burying the Shadow are haunts created by strong emotion and they usually take the form of the local superstition. Essentially, if you believe your house is haunted, your house is haunted.
The Book of Lost Things: Much of the world is derived from David's and Jonathan's fears. The Loups were created from the latter, so when Leroi finally kills Jonathan, he (as well as the rest of the Loups), falls apart and ceases to exist.
In Kroniki Drugiego Kręgu very talented Illusion Weavers can create illusions so convincing that one's body feels it like a real thing. One character accidently burns another, while trying to scare him off with a fireball. Apparently frogs are too stupid to fall for this trick.
"First Person Shooter", written by William Gibson and played for comedy, like the entire episode.
A more serious version is the episode "Pusher", where a man has the ability to talk people into killing themselves in various ways. Most of the time, it's by making them do something self-injurious, but at least one of his victims dies from being given a graphic verbal description of a heart attack, and then suffering the same.
Another example was in "Scary Monsters" in the final season. A young boy causes several people to kill themselves when his illusions are made real in their minds. Luckily John Doggett is too stubborn to believe and tricks the boy by using his imagination against him.
Sliders did an episode that ripped off Nightmare on Elm Street, but with these evil nerds that called themselves "The Dream Masters". The nerds were defeated once the characters banded together, realizing that it was all just a dream, and overpowered the nerds' minds, resulting in an inability to be harmed. There was a moment where Rembrandt is cornered by the nerds and is about to be killed. He goes, "I wish I had my gun right now." The gun materializes in his hand, and he blows a few nerds away. Strangely, when we last see the nerd who tried to hit on Wade, he is walking into the room with his sleeve on fire. It's not clear how that happened. Maybe he was sitting near a candle and jerked his hand.
The classic episode of the Star Trek: The Original Series, "Spectre of the Gun", has the landing party trapped in a surreal nightmare that recreates the Shootout at the OK Corral. Spock realizes the whole experience is an illusion that is only as real as their minds accept it to be, but, as McCoy says, only someone as emotionless as a Vulcan could have the iron-hard certainty required — even a shadow of doubt would be lethal. Spock mindmelds with the others to make them just as sure of the illusion as he is, making them invulnerable to it.
In "Shore Leave", the planet creates whatever the crew thinks of - whether it's an old Academy nemesis, a Japanese warplane making a strafing run, or a Samurai warrior. Kirk realizes this and orders the crew to come to perfect attention and focus on nothing but standing absolutely stock-still and staying that way, removing all of the illusions.
The TNG episode "Interface" has Geordi controlling a probe with his VISOR. When a fire suddenly engulfs the probe Geordi's hands are burned by the interface suit he's wearing.
In the Deep Space 9 episode "Things Past" several members of the crew were in danger of this, and Garak even got a bloody nose.
In Voyager, in the episode "The Thaw", the crew of the Voyager finds a machine where the surviving members of a species whose planet was struck by a natural catastrophe were placed in stasis, and their brains were wired into the machine, which created an artificial paradise inside it. Unfortunately, when the crew looks inside the program uploading Harry inside it, they find out that inside there is an... entity, called "The clown", who keeps the dreamers trapped inside. When the crew tries to disconnect them from the machine, it threatens to put one of them on the guillotine. He does, and the dreamer's body dies of an heart attack.
One episode of the original Twilight Zone, "Perchance to Dream", justified this: the character at risk of death was suffering from a severe heart condition, bad enough that having a particularly scary nightmare would give him a lethal heart attack. Unfortunately for him, his last few dreams appear specifically designed to give him said heart attack...
One episode of the most recent version (2003 series) of the Twilight Zone, aptly titled "Placebo Effect", featured a doctor dealing with a chronic hypochondriac patient. Normally keen on giving him placebos, she's horrified to find he actually IS showing signs of a terrible, previously unheard-of disease. It turns out that the disease was fictional, and after reading about it in an old sci-fi novel, the hypochondriac somehow "made it real" by believing he suffered from it. Soon, everyone in the hospital has caught the disease and appear to be near death. The doctor manages to cure him, and thus everyone, by telling him that a meteorite crashed which contained an antidote for the "space virus." By believing her, he is cured. However, pessimistic thoughts overwhelm him, and he believes the crashed meteorite will create a new Ice Age and destroy humanity. The final shot shows the nurse motioning the doctor outside, to see the the city besieged by a massive blizzard.
Stargate SG-1 episode "Avatar": Teal'c gets trapped in a VR simulation that shocks him every time he dies in the game. While the simulation itself can't harm him, the continual shocks force his body to produce extra adrenaline, which eventually can kill him. He's trapped because in real situations Teal'c would never quit, and so the simulation disables the abort option.
It's worse than that: the simulations aren't pre-programmed, but work off the sim runner's mind. Teal'c will never quit, never surrender... He also believes, at the time, that no matter what, they can never fully defeat the Gou'auld. Meaning not only can he not just hit the off button, but whenever it seems like he's going to win something new pops up, kills him, then the sim restarts and gets harder still.
Stargate Atlantis episode "Doppelganger". Dr. Heightmeyer dies in her sleep after dreaming that she fell off a balcony onto a pier below. There were other factors involved in that death....
Lois and Clark has an evil genius who traps the main characters in a VR system. In the end, the system is shut down while he is still hooked up (and "downloaded in"), resulting in his mind being separated from his body, and the last shot is him screaminginside a computer screen.
Another episode had a master hypnotist (the second master hypnotist, not the first one) whose hypnotic illusions were so real that Jimmy bumped his head on an imaginary desk and got a real life bruise. The hypnotist used this power to cause people to die from illusions.
Subverted in Eureka. During an episode of shared dreams, one Red Shirt died in reality and in the shared dream at the same time... but it turned out to be coincidental.
In VR 5, dying in VR does not kill you, but it leaves you brain-dead. (In fact, it's claimed that dying in something as primitive as a flight simulator will have this effect!)
Lexx: "Patches in the Sky". We're told, offhand, that "If you die in a dream, you die for real," as if it's obvious.
War of the Worlds: "Totally Real", the loser of the VR game lost his life — though this turned out to be the entire point of the simulator's design.
In "The Deadly Assassin", the Gallifreyan Matrix works like this, as death in the virtual reality overloads the person's mind. (In "The Trial of a Time Lord", on the other hand, the Doctor and his opponents physically enter the Matrix. Don't ask.)
In "The Three Doctors" Time Lord Omega is essentially the god of an antimatter world he's imprisoned in within a black hole. Despite having been destroyed by the singularity's energy, he still exists because of his belief and desire for himself to still be alive.
In "The Mind Robber", it is established that the inhabitants of the Land of Fiction are, well, fictional... unless you believe in them, in which case your mind makes them real and they are able to harm you. Strangely, though, in order to get rid of a menacing fictional character, all present must vocally disbelieve. The Doctor and Zoe are able to make a Minotaur vanish this way, but Zoe's inability to disbelieve in Medusa forces the Doctor to use a mirror to defeat her, even though he knows she's fictional. Later, Zoe is forced to fight Karkus, whom she knows is fictional, because the Doctor has never heard of him and thus cannot disbelieve.
However, in the New Series episode "Amy's Choice", this is explicitly subverted by the Dream Lord, who explains that if you die in the dream, you wake up perfectly healthy in real life. The only risk was trying to figure out which was the dream and which was reality, because if you die in reality ... well, you just die.
Supernatural did this twice. The first was a demon born out of a Deadly Prank and who kept existing because of people believing in him and the second was this dream-trope in a nutshell.
Searies 2 of Torchwood had a villain who only existed in the altered memories of the staff. He faded from existence when they used the humorously named drug retcon to erase their memories of the time he'd been interacting with them (all of two days, though he himself had retconned the staff's memories to include him further back. It only required 2 days erasure to get rid of him, though, because obviously the memories he put in or stirred to the surface were only that much fresh).
An episode of Charmed featured a man who could enter dreams, and when women rejected him he killed them there.
In a recent episode of Heroes, Matt telepathically enters Angela's mind to free her from her comatose state. Arthur uses HIS telepathy to put an image of Daphne in Matt and Angela's shared mind world thingy. This imaginary Daphne stabs Matt in the stomach. When this happens, the real world Daphne, who's right next to Matt, realizes that Matt has a stab wound right where mind-Daphne stabbed him. However, when Angela (trapped in her own mind) convinces Arthur (who personally entered her mind near the end) to free her and Matt, Matt awakes and the stab wound is gone.
M*A*S*H The camp runs out of painkillers. All the doctors get together to convince the pain-wracked patients that these "sugar pills" are very new, very effective painkillers. It works.
It is called the placebo effect.
Fringe had an episode where a man was killed when a drug convinced him that an assassin was slicing his throat, causing a slash through his neck to appear in real time.
In the season three episode of House called "Airborne", Cuddy becomes sick during a flight from Indonesia to the US, having rashes, nausea and a fever, all because she believes she's been infected with meningitis from another passenger. Who turned out not to have meningitis at all.
An episode of The 4400 features all of the main characters being trapped in a shared dream where they had to escape from a building that was trying to kill them. This trope is brought up in that the characters don't know whether it's going to be subverted or played straight. It's subverted; after Shawn is killed by an exploding window and Meghan is electrocuted, both wake up fine at the same time that the others are released.
An episode of Medium has Alison suffer the same injuries in real life as she had in her dreams, making her afraid that she would die in reality if she were to die in her dreams. It didn't help that she was dreaming of a Zombie Apocalypse.
In Dollhouse, if, while in the Attic, you are killed in your mindscape, your body dies. Used as a means to escape the Attic by Echo, by dying and using the time being unplugged to get out.
In Thousand Ways To Die, there is a story about a woman who had persistent nightmares of a small, demonic imp strangling her. While she thought she was being strangled in her dreams, her physical heart raced till the point of a heart attack, killing her in her sleep.
An Outer Limits episode has scientists inventing a new device that allows people to share dreams and cure people's mental problems. The protagonist and her boyfriend use the machine to enjoy a romantic dinner. However, after that, he goes into a coma. The machine is blamed, and the project is shut down. However, she accidentally gets messes up the implant injection (it latches on directly to her brain instead of a nerve in the palm), which allows to her mentally interface with anyone she touches. She interfaces with the boyfriend and finds out that he's allergic to strawberries, so when they ate them in the vivid dream, his body reacted as if he actually ate them for real. She "cured" him by convincing him that she has a cure in her hand and feeding it to him in the dream.
Adventures in Odyssey: This seems to apply to all of Whit's virtual reality inventions, the Imagination Station being the most frequently used. At least, if a hacker got a hold of the controls and changed the adventure to put you in the crossfire of cannonballs, the threat was very real, just like threats during the adventure from, say, a ruler who would have you executed for refusing to bow to false gods.
The Big Finish Doctor Who audio adventure "The Mind's Eye" is a textbook example, with the local flora putting Erimem and Peri into a dream-like state (the Doctor isn't ultimately that affected), where they will die for real if they die in their "dream".
The RPG Shadowrun uses the "lethal biofeedback" version in its cyberspace; however, a hacker can avoid the feedback by using what's referred to as a Cold ASIST interface (as opposed to the Hot ASIST interface that most deckers use). However, not only does Cold ASIST forgo all the massive bonuses to your die rolls that Hot ASIST grants, (which is why hackers use Hot ASIST, despite Cold ASIST being the default user mode for all legitimate users of neural interface technology), but all the other deckers will mock you viciously before they Curb Stomp your Nerfed tuchas. One of the major events of the metaplot had the Matrix crashing, which resulted in people either dying or suffering irreparable brain damage when their cyberpersonas were cut off from their bodies. Considering the fact that deckers directly connect their brains to the Matrix, this is at least somewhat more acceptable than other reasons.
Dungeons & Dragons has several illusion spells (most notably of the Shadow sub-school) that function this way, e.g. Shadow Conjuration and Shades. These spells create illusory constructs or facsimiles of spells from other schools, and have reduced effects on characters that successfully "disbelieve" them. Naturally, they always have this reduced effect on objects and creatures with low intelligence, such as constructs.
Some Phantasm spells, such as Phantasmal Killer and Weird, make you save or die upon failing the roll to disbelieve, doing nasty damage even on success. Annoyingly, Death Ward, which protects against other spells that make you save or die, won't protect you against this because it's an illusion based on fear.
Probably because Death Ward protects only against direct, external magical energies that cause death while these illusions essentially rely on tricking the target into killing itself.
One of the first Dragonlance game modules had the player characters travel into a living nightmare to end its hold over an elven kingdom. Many of the monsters the players encounter are in fact creations of the dream, and can be made harmless if players state they don't believe in them. Unfortunately, quite a few of those monsters are very real, and will attack the players anyway, and it's very difficult to tell the difference.
Some D&D-based literature describes the physical threat of illusions. Trollshead (in The Dragon, #31), describes how some people ran through the illusion while others were burned alive and left charred.
The psionic powers "Recall Agony" and "Recall Death" cause the target to see into the future - specifically, to witness a possible future in which the target dies horribly. This can cause the target to die horribly.
Can happen to you in Mage: The Awakening with the Astral Realms. Under normal circumstance, attacks in the Astral Realms don't harm health, but instead reduce Willpower (a person's reserve of mental and emotional strength). If a person loses all of their Willpower (not necessarily from being attacked) they return to the waking world, unable to maintain their Astral self and completely emotionally drained, but otherwise unharmed. There are however ways in which the person can be damaged or destroyed mentally. For example, being attacked by an ideology until the person's identity is completely buried beneath fanaticism, being drawn into the hold of an insanity realm until one's personality is utterly destroyed from that insanity, or going to the Dreamtime unprotected, where one's mind will be completely washed away by a consciousness which is incompressible to and uninterested in human perspective or individuality (essentially, your sense of identity is lost among the thoughts of something which has existed before there was life). In these cases, the body becomes a completely healthy vegetable. There are also beings capable of inflicting actual damage from the Astral Realms, though this is more to do with magically being able to target your body directly rather than because Their Mind Makes It Real.
The "stigmata" enhacement to the Illusion advantage from GURPS: Powers can cause small amounts of damage to the target, but only to the point that he falls unconcious from the wounds.
Continuum - Roleplaying in the Yet. When two characters meet while Dreaming any combat between them is usually harmless - any character who is knocked unconscious or killed just wakes up. However, if one or both of the dreamers uses Telepathy during the combat the damage inflicted is real and can result in nerve damage (and paralysis when the victim awakens) or death.
Half of Catherine's story and gameplay revolves around a series of dreams where you have to constantly climb a tower that is slowly collapsing from the bottom up. If you fall off (or die in any of the other myriad of possible ways), you die in real life.
The eponymous virtual reality program in Sam and Max: Reality 2.0, works like this, and our heroes take advantage of this to solve at least one puzzle.
Arguably used in the Silent Hill series. How much of the games is real and how much is illusion is hotly debated. It's implied that the twisted, blood-and-rust-soaked Otherworld, at least, is a kind of hallucination, especially in the first game, where it's stated that several police officers who went to investigate the titular burg mysteriously died of heart attacks. Most likely they wandered into the Otherworld and fell victim to this trope. What people are actually doing while trapped in the nightmare, however, is another matter entirely...
Though not really part of the main storyline, Silent Hill fans and players have created a theory that there really are no monsters or cults in the town of Silent Hill. Rather, YOU, yourself, are the monster. Even more fucked up, it was said that there are some kind of plants that grow naturally within the vicinity of the town, which induces insanity and paranoia, which makes you think that you are being chased by all sorts of fucked up creatures in the town and makes you go into a murder-spree.
In Fatal Frame/Project ZERO 3, "The Tormented": Rei, Miku and Kei travel into the House of Sleep when they dream. If they lose all their spiritual health in the dream-world, they are confined there forever; leaving nothing in the physical world but a bunch of scorch-marks.
Central to the gameplay in Dystopia, where players work with each other between Meatspace (the solid world) and Headspace (Cyberspace). Headspace obstacles such as encryptions, passwords, or ICEs (Although the regular ICEs don't damage the player, and GREEN ICEs only forcibly jack the player out with an EMP) are physical to the player's avatar, and entire fights wage on in Headspace. If one dies in Headspace, they are yanked back to their physical bodies with disorientation and bodily damage (HP loss). It is also possible to sneak behind a jacked-in player in Meatspace and kill them. The player's avatar is told that their Meatsack (body) is taking damage, and death simply deletes the Headspace avatar in the middle of whatever it was it was doing.
Played straight as an arrow in the DLC, Operation: Anchorage. If the Lone Wanderer dies in the Anchorage simulation, his/her body goes into fatal cardiac arrest in the real world. Justified by the Brotherhood of Steel being unable to re-enable the safety features in the simulation. As for why a stated training sim would have lethal settings, it's repeatedly hammered in that the head of the dev team was a nutcase.
In the PC adventure game Ripper, the killer known as the "Ripper" has the ability to kill anybody who once played the online game Ripper (the "Ripper" is one of the original players, the protagonist has to figure out which one of the surviving players it is). The Ripper's ability takes the form of a "software rewrite" of the victim's "brain software": the hormonal and electrical layers of the human brain. When triggered (through use of a Brown Note telephone call), the fluid and air pressure within the victim increases rapidly causing them to violently explode. The protagonist has to have his own "software" modified with an immunisation so that the Ripper can't use the "long range doohicky" any longer (he is still vulnerable if the Ripper chooses to attack him "face to face" in the virtual world).
Later, the Ripper calls all of the surviving characters into the virtual world, and demands the protagonist choose who they think it is. The protagonist at this point has armed himself with a single-use "virtual weapon" in the form of a pulsing orb of energy. Each of the characters make their case to the player, and the player must use the virtual weapon on the character they think is the Ripper, presumably killing them, as the ending narration is spoken in the past tense. Choose badly and not only have you killed an innocent person, the Ripper attacks the protagonist directly and kills him as well.
In Iji, you can "crack" computers and enemies with your nanofield, but if you fail the crack you are booted out by your target's security system with negative effects depending on the difficulty of the crack. Especially odd since it's not virtual reality. I assume the computer interface is just that realistic. On the other hand, you are standing right next to whatever thing you're trying to hack and, in fact, probably touching it, so it could just be zapping you. Also, doors mostly just increase their security, and supply crates will break or explode as retaliation, and enemies mostly just realize you're standing there and stop standing around in a peaceful manner. And maximizing your crack level removes all harmful effects of failure.
Weirdly played with in System Shock: being kicked out of cyberspace doesn't cause much injury, but does max out fatigue (physical exertion).
Shadow the Hedgehog has two levels that take place in Shadow's memories, trying to help people aboard the space colony ARK, which went out of commission fifty years ago.
Eternal Darkness gives you a Sanity Gauge that, when low, will cause hallucinations that are often freaky, but ultimately harmless. However, when your Sanity Gauge has run out entirely, anything that would normally only reduce your Sanity will start taking chunks out of your health instead, most likely due to this trope.
The plotline of Professor Layton and the Diabolical Box. The box contains some hallucinogenic gas that makes people experience what they expect, including death. This was the whole illusion of Folsense, as Luke and Layton had seen pictures of 30-year-old Folsense beforehand, and so perceived it that way when they got there. Truth was, it was pretty decrepit.
World of Warcraft brings us Vanessa Vancleef, who poisons your party and sends you a few rooms back, the poison causes you to hallucinate various nightmares involving past bosses, despite nobody actually being there, dying to the fire/ice/lighting/bosses themselves makes you drop dead in reality.
Possible example in inFAMOUS, when heading into a tunnel to destroy a tanker of tar, at one point you begin to hallucinate, seeing enemies fading in and out of reality and much larger than they should be. But they aren't just hallucinations, as their bullets still hurt you and can still kill you.
In Mark Of The Ninja, the enemy ninja in the final level show up as the same kind of Mook the player has spent most of the game killing due to the main character's hallucinations: due to this trope, their nonexistent machineguns have the same degree of range and lethality as genuine article.
Then again, since the main character never actually fights other generic ninja during the game, it's hard to say how their normal abilties would match up to their counterpart, although it's pretty safe to say that they don't have access to any equipment that'd duplicate the effectiveness of a sniper rifle.
In Perfect Dark Zero, Zhang Li's custom Deathmatch VR rig kills the defeated player for real, unless they are disconnected before in-game death, as with Mai Hem.
In Don't Starve, if your Sanity Meter drops too low, your character will start hallucinating... and their hallucinations will begin to affect reality. Sets of shadowy disembodied Night Hands will try to snuff out your campfire at night, rabbits will turn into hairy little monsters named Beardlings that drop Beard Hair instead of Morsels of meat, and eventually the flickering shadowy creatures you sometimes see start spawning as Crawling Horrors and Terrorbeaks.
Indigo Prophecy does this so many times you'll lose count. It's never quite explained why, but Lucas hallucinates enemies and other supernatural threats like sentient wind at least once every two levels or so. Failing to escape them generally ends with him going into a coma-like state.
Perimeter: Totalitarian-sect-likeness of Exodus is traced back to first attempts of humanity to explore the worlds of The Chain. The violent reaction of the worlds themselves (termed "The Scourge") was tied to chaotic and fearful thoughts of inherently flawed humans, so the ritualistic practices, networked meditations and other means to keep reins were put in place. Without those, a high concentration of people (which Frames are) could never hope to survive. Other factions abolish this, one remains under the radar by going cybernetic hybridization way instead, the other embraces The Scourge.
In a Metroid-based webcomic called Metroid: Third Derivative, Samus is "uploaded" to the Space Pirates' main computer, and put into a training simulation by a mostly-friendly pirate. Samus asks the Pirate, "And I suppose if I die here I die in the real world too?" The Pirate answers, "What? No. That's stupid and completely defeats the point of virtual training." To which she replies, "Chalk up a rare victory for common sense then."
Subverted in 9th Elsewhere: The character who is actually asleep, Carmen, is perfectly safe inside her own mind. The muses who journey with her, on the other hand, can fully manifest themselves in her mind, and therefore can have harm done to them, and they need to eat, breathe, and sleep, unlike Carmen.
SCP-896 ("Online Role Playing Game"). Anyone who plays SCP-896 will have their real life attributes increase to same degree that their in-game attributes do. However, if one of a character's attributes rises too high above the others, the player's attributes decrease.
The Slender Man is theorized to have been created by this, coupled with lots of stories so the universe can fit him into history. Some people have recently begun to theorize, mostly because of the Slender Man stabbing incidents coupled with unusual occurrences in their general area (i.e. Children playing outside in the middle of the night) that thistheorywascorrect.
The Simpsons episode "How I Wet Your Mother" parodies Inception with Professor Frink's device that allows Homer's family into his dreams. They die in the dream, they die for real.
In the "Nightmare on Evergreen Terrace" segment of "Treehouse of Horror VI", an undead Groundskeeper Willie haunts Springfield Elementary students' dreams and kills them at weak moments.
Kim Possible has an ep involving a VR system, where its malfunction resulted in extreme aggression if the players were removed without winning the game.
Subverted in Batman: The Animated Series, "Perchance to Dream", as Bruce escapes from the Mad Hatter's dream world by deliberately leaping to his "death" from a tower, causing himself to wake up in the real world. However, in the exact same series, The Riddler hooked Commissioner Gordon up to a virtual reality computer program that could do such a realistic simulation of high-G loads, that Gordon's physical body would think it really was happening and suffer cardiac arrest. In the same episode, Riddler himself gets his brain fried when the computer crashes while he's still hooked to it.
Code Lyoko is an exception, sometimes; when Ulrich, Yumi, or Odd lose all their Life Points, they are merely rematerialized into the real world. If this happens, they simply return to the material world too weak to stand up. Also, thre's a twelve-hour cooldown between respawns. However, this return only works when the scanners that allow access to Lyoko are functional. Also, Aelita, who was tied to the computer for the first two seasons, would have been lost forever if she ran out of Life Points. Unsurprisingly, she was never actually devirtualized until the tie was broken, but plenty of times after that. Also, it appears that no matter who you are, falling into any of the Bottomless Pits surrounding the areas appears to prevent you from ever coming back. On several occasions, someone attacks their own ally to prevent this from happening.
This abyss is referred to as "The Digital Sea"—essentially a representation of the raw networks that are outside the control of the Supercomputer which runs Lyoko. Any persona that fell in would be scrambled beyond the ability to reconstruct it, thus the danger.
Parodied and possibly subverted in the Futurama episode "Parasites Lost". When most of the Planet Express crew take a "Fantastic Voyage" Plot through Fry's body, it isn't the actual chacters who go on the trip. They are are actually nanobots remotely controlled by the crew interacting with a VR simulation of Fry's innards. Toward the end of the episode, Leela chops the other characters to bits with an axe while they're all still in tiny robot mode. Immediately afterwards, we see the actual characters taking off their virtual reality equipment back at the office. When someone asks if everyone is okay, they cheerfully agree that they are.
Foreshadowed in a previous episode; the internet is fully VR and dying in the 'video game' section just causes extreme annoyance.
In Teen Titans, Robin is exposed to a hallucinogen that causes him to see and fight Slade, and received real injuries as a result. Whether or not those injuries were an example of this, or merely him beating himself up while hallucinating, is not entirely explained.
Raven: "I don't know if he's real or not. But he's real to Robin, and that's all that matters."
Transformers Animated, "Human Error Part 2": The Autobots realizing that they're in a computer simulation set up by Soundwave, manage to change their human bodies back to their Cybertronian ones by thinking about it. Amusingly, Bulkhead can't until he makes the transforming noise with his mouth.
W.I.T.C.H.., "E is for Enemy", has this trope in action.
In Young Justice, this is what happens in the episode "Failsafe" when it was supposed to be a mental simulation that had Gone Horribly Wrong. It went From Bad to Worse when M'Gann was so overcome by Artemis' "death" that she unintentionally rewrote everyone's memories so that the team forgot it was a training exercise and slipped into a real coma when they "died".
Certain Indigenous Australian tribes have a death curse for criminals that involves wrapping a piece of the cursed person's hair around a kangaroo bone and performing rituals over it. A special shaman hunter then finds the person and points the bone at them.
Similar claims have been made of some believers of Vodoun in Haiti and Africa. It is believed by some that Christianity has affected some people strongly enough to cause psychosomatic stigmata to form on their palms, as well (the real wounds of cruxifiction would be on the wrists, by the way).
Hypnotic suggestions work this way. It is possible for somebody in a deep hypnotic trance to feel things that are not present, which leads to some real-life Power Perversion Potential.
The Placebo Effect. Believing that you are taking medicine causes you to experience a reduction in symptoms and occasionally the cause of the symptoms. It bears mentioning that Placebos seem to have something like a 60% effectiveness rate. Even on cancer.
One anecdote is that a nurse in World War II had run out of morphine and had to stabilize a wounded soldier to keep him from going into shock. She filled a syringe with saline (salt water) and injected it in, telling the soldier it was morphine. It worked.
Of course, they can't replace real medicine; their best use is for alleviating the pain of recovery. Sadly, this would need your doctor telling you that the sugar pills he's giving you are a miracle dug and not sugar pills, which is completely unethical.
Applied in the theological theory of Pandeism: miracles and revelations occur not because a God is watching over us and intervening, but because the Universe-creating entity has become us (and the rest of the Universe) and believers in any religion are able to unwittingly tap into their own little bit of Creator-power.
It doesn't actually make it real, but this is the belief for many sufferers of OCD, who have intrusive thoughts that if they don't perform actions and rituals terrible things are going to happen. They don't nor ever will happen, but the sufferer can believe that their brains belief will make it real, so they do it just to be safe.
In general, its been proven that we're pretty easy to fool in this regard. A newer type of prosthetic limb channels physical feedback from the prosthetic to the stump. It doesn't take long for your mind to associate that stimulation with your prosthetic to the point that it feels like your actual limb. Also, VR can make you think a virtual image or a displaced image of something else is your real body. Our brains are built ready for cybernetic upgrades.
And for the matter, unrelated studies and effects can offer interesting insight in to how much our brain fools us. During one brain surgery, one patient felt the presence of a non-existent person 'nearby'. Follow up tests/cases shows that a part of the brain responsible for the sense of personal location within 3d space was being triggered and manipulated resulting in people sensing and seeing what amounts to classical depictions of dopplegangers.
Hysterical Pregnancies tend to make humans/animals experience all of the symptoms of being pregnant including an expanded stomach area as well as a baby kicking (called "quickening"). These women believe they are pregnant.
In the same vein is Couvade Syndrome or a Sympathetic Pregnancy where the husband will experience labor pains, cramps, morning sickness, and other symptoms of pregnancy, although a man doesn't normally believe he is pregnant.
It's been suggested that Grigori Rasputin, the Russian monk who gained access to the court of the Russian Empire by supposedly being able to treat the Tsar's hemophiliac son, hypnotized the boy to "cure" him whenever he was injured. Rasputin's hypnotic powers were in fact recounted by others, even hardened men like some of the Tsar's ministers. Either Peter Stolypin or Sergius Witte who later recounted Rasputin's attempt to hypnotize him, which was very nearly successful.
Rasputin's treatment to hemophilia is now believed to be far simpler than hypnotism: he told the Tsar to give up the modern medicine with his son's case, which at the time included dangerous amounts of aspirin, which today is known to actually make the effects of hemophilia worse. No wonder the boy got better.
Somatoform Disorders can cause this to happen. One of the earliest diagnosed Somatoform Disorders is "Conversion Disorder", which causes a person's psychological stresses to be converted into physical pain.
Inverted with trauma shock (albeit temporarily), where your mind's refusal to consciously accept that you've just been torn to bits keeps the pain at bay until you either pass out or cool down a bit.
Rather, your brain has accepted the fact that you are injured, but it also realizes that whatever it is doing right now is more important to your survival, and so it starts producing painkilling neurotransmitters until what you are doing is finished.
A Nightmare on Elm Street was inspired by studies of this and similar cases. A number of healthy middle-aged immigrants died in their sleep from heart attacks. After checking and rejecting every cause they could think of, the investigators concluded that the diseased were scared to death by nightmares.