When a character is ill, delirious, hurt, drugged or otherwise mentally compromised, they will often assume another person coming close to them is someone recognizable to them:
- Mistaken for Loved One: The person may mistake them for their family, friends, comrades, a mentor or student. Often, the implication is that they think said loved one is there to help them. The "helper" will either play along to comfort them (especially if they're dying), or try to explain their real identity. It becomes dangerous if they mistake an enemy for a loved one.
- Mistaken for Enemy: This usually happens when they get delirious in the midst of battle, often mistaking their comrades coming to help them for a foe trying to finish them off. Or when the delirious one is suffering from Brainwashed and Crazy, FaceMonster Turn or similar, their newly conditioned mind will make them think that everyone's out to get them.
Often the confused person will be so out of it they won't pay any attention to the other person's words as they try to explain their true identity.
When the deliriousness is caused by hypnotism/illusion (often a common tactic for a Master of Illusion) or hallucinogens, there could be a plot centered on how to stop these influences.
A common variant of this trope is for a ghost (or other type of undead character) who has Unfinished Business to mistake living people for someone they knew when they were alive. Ghosts are often found harassing people who bear a vague resemblance to someone they knew while alive, people who share their other qualities, or just flat-out everyone they encounter.
See also Set a Mook to Kill a Mook for when this is exploited - by making the mook think the other mooks are their enemies.
Subtrope of Mistaken Identity.
- The Psychopathic Manchild Miata in post-Time Skip Claymore comes to view her partner Clarice as her surrogate mother (after Clarice is forced by awkward circumstances to breast-feed her).
- Played for Laughs in One Piece Film: Strong World. Shiki sometimes mistakes his subordinate Scarlet for his mother.
- Bleach: Aizen once subtly trapped Hitsugaya and others in his illusion shikai, making them believe that his subordinate Momo was Aizen himself. It didn't end well: they almost kill poor Momo under such effects, and Hitsugaya has a screaming Heroic BSoD when he realizes it.
- In a Code Geass gag comicnote , Suzaku, half asleep at a school slumber party, mistook Rivalz in a Zero costume for the actual Zero. Rivalz ends up in the hospital.
- Played for Drama in Basilisk Kouga Ninpu Chuu: As Hotarubi loses her fight with the shapeshifter Saemon and is fatally injured, she mistakes him for her boyfriend Yashamaru, whom Saemon had been impersonating. Saemon allows her to die thinking that he's Yashamaru, who had died few ago.
- After being poisoned in a botched assassination attempt in Your Son, a delirious Edward mistakes Mustang for his father, thinking he finally came back. Mustang, already feeling guilty due to being the assassin's intended target, plays along.
- In The Ripple Effect, Eric tries to kill Jerrica but he accidentally attacks Deidre in his mentally ill state. He can't tell the difference between the two blondes.
- A feverish and near-death Roy in The Planets mistakes Winry for Riza. Riza's recent death was the entire reason he lost his arm in the first place.
- So We'd Both Be Free: On his deathbed, an ill Ozai mistakes his daughter Azula for her mother Ursa.
- In Familiar Taste of Poison a feverish Steve mistakes Tony for Howard before falling unconscious.
- Dear Diary: A dying Prima mistakes the Audino nurse for Opal, who was forcibly kept away from her. The nurse decides to go with it to let her die happy.
- In Atonement, Briony, working as a nurse during World War II, is asked to sit with a dying soldier to keep him company. The soldier mistakes her for a girl he'd met years earlier, and she struggles to play the role for him.
- This is a Running Gag running gag throughout the Back to the Future film series, with Marty blearily waking up in a number of strange beds and saying "Mom? Mom, is that you?" Subverted in that at least once the person with him was his mother - albeit somewhat younger than he'd anticipated.
- In Hurricane Gold, Manny hits his headly badly and becomes delirious because of it. This causes him to think that Bond is his long-dead brother, which Bond uses to his advantage.
- In Dragon Bones, Ward's constantly drug-addled (to the point that one can assume her brain is damaged) mother mistakes him for his own father. In a more dramatic example, Oreg, who has been a slave to Ward's male ancestors for centuries mistakes him for a man that had treated him very badly, while he is having a PTSD-triggered flashback to the time when it happened. He can't hurt Ward physically, but this moment is when Ward realizes that this nasty ancestor was his worshipped idol, the one he wanted to be like. Not anymore. Oreg later tries to comfort him by pointing out that the guy wasn't all bad, but it doesn't help much, as that was Ward's only role model.
- Honor Harrington: In The Shadow of Saganami, a minor character, severely injured after a Marine raid, mistakes a Manticoran doctor for his superior in the Kornatian resistance and tries to give him a report. While most of the report was incomprehensible even with Manticoran sound enhancement tech, they made out enough to blow the Mesan Alignment's plot.
- In A Song of Ice and Fire, Robert Baratheon, very drunk after his own wedding, misidentified his new (arranged) wife Cersei Lannister as his true love interest, Lyanna Stark. This made Cersei hate him and totally ruined their chance to build anything resembling a loving family... which later led to very serious political consequences, because, you know, they were king and queen of Westeros.
- Sword of Truth: In Temple of the Winds, when Cara is rendered catatonic by Jagang, a hooded healer comes to treat her. Once Cara opens her eyes, she looks at him and asks "Lord Rahl?" (that is, Richard). The man immediately lowers his hood and announces himself to be Drefan, Richard's half brother. At first, Kahlan is confused why Cara would mistake him for Richard (the family resemblance is strong, but not that strong), but then realizes she mistook Drefan for Darken Rahl, Richard's Evil Overlord father, whom Drefan resembles much more.
- Babylon 5:
- In the episode "Shadow Dancing", Stephen Franklin is delirious from loss of blood and hallucinates that the medical orderlies wheeling his stretcher into Medlab are Delenn and Sheridan.
- The first season episode "And the Sky Full of Stars'' has Sinclair being kidnapped and forced into a drug and cyber induced hallucinogenic state which forces him to relive his missing 24 hours after the Battle of the Line. When he finally breaks free of it, he starts wandering around the station, but whenever he sees anyone, he thinks they're robed Minbari, causing him to shoot at anyone he encounters, except for Delenn, who he realized was there as part of the Grey Council when he was captured by the Minbari, and gives him the clarity of mind to snap out of it.
- In an episode of Buffy the Vampire Slayer Willow is unconscious in a hospital room and Xander is sitting with her, finally telling her how much he loves her. Then she wakes up, and thinks that it was her boyfriend Oz talking to her.
- Happens briefly on Cheers when Sam tries to hotwire Cliff's car and gets an electric shock for his efforts.
Frasier: Sam, are you alright?
- Played for Laughs in El Chavo del ocho. While Sleep Walking, Doña Cleotile mistakes Don Ramón for her "yellow-chested sparrow" who recently escaped its cage. Not like she's complaining anyway when she wakes up and realizes the mistake.
- Doctor Who: In "The Empty Child"/"The Doctor Dances", the titular child, mortally injured by a bomb and brought back wrong by alien nanotechnology, can only say "Are you my mummy?" while transforming anyone he touches into a copy of himself. This case is more than it seems, however, as it turns out that one of the people he's haunting really is his mother.
- An episode of The Dumping Ground has Gina, one of the careworkers, bring her mum, who is suffering from Alzheimer's, to Elm Tree House. At one point, Hattie (Gina's mum) is giving a shopping list and grabs hold of Faith's arm (one of the kids), mistaking her for Gina, telling her where not to buy the food. Faith, however, keeps her cool and tells Hattie she understands. Later in the episode, Hattie goes missing from Elm Tree House and is found at a bus stop. Faith pretends to be Gina in front of Hattie, which she falls for, to convince her to come back to Elm Tree House.
- A Played for Laughs example from Gilligan's Island. The Skipper poses as a hostile native to get the Howells back together after they have a fight and gets hit on the head. He staggers off. Gilligan goes after him and asks Skipper twice if he's all right. The second time he says, "For the last time, I'm all right, Mary Ann!"
- British comedy The IT Crowd:
- In the very first episode the character Roy receives a major head wound and proceeds to call fellow character Moss his mum, before thinking a phone is ringing, picking up and answering something that wasn't a phone, then lying down on the floor.
- And in the same series of the show, Roy calls a psychiatrist his mum after sleeping with her, which the psychiatrist finds "very interesting". Earlier in the episode when he first met her he had commented on how much she looked like his mom. It became somewhat of a Running Gag for the episode.
- One episode of M*A*S*H had a dying patient mistake Nurse Kellye for his girlfriend from home.
- Another episode plays this for laughs when a sick and delirious Frank mistakes his lover for his wife.
- Downplayed in an episode of NYPD Blue. The main character for the first season was John Kelly, who got Put on a Bus partway through the second season. There is another character named John Irvin who is a PAA (civilian aide) working in another part of the 15th squad building. Detective Martinez has been shot and is going to go into surgery. John Irvin comes by the hospital and gives a cross to Martinez's partner Medevoy to pass along to him, saying it's good luck. When Medevoy gives the cross to Martinez and says it's from John, Martinez asks "John Kelly?" Medavoy replies no, it was Upstairs John.
- In an episode of Smallville Clark is very sick with a fever. Chloe comes over and pours her heart out to him in a letter. He says just one word - Lana, the one he is in love with. Crushed, Chloe leaves.
- One episode of Space Cases saw Radu and Bova trapped on a shuttle and running out of oxygen. Suffering from oxygen starvation, Radu starts hallucinating that Bova is Suzee, who's back on the ship.
- In the British mini-series To the Ends of the Earth, protagonist Edmund Talbot receives a concussion and spends a considerable amount of time in bed dreaming/hallucinating. He wakes up briefly at one point with one of his fellow passengers bathing his forehead and mistakes her for his old governess.
- In the Stargate Atlantis episode "Phantoms", Sheppard, hallucinating under the influence of an alien device, mistakes Teyla for his wingman who was killed in action in Afghanistan and McKay and Ronan for Taliban soldiers, so he tries to protect her and attack them.
Sheppard: I'm sorry for shooting everyone.
- The premise for Injustice: Gods Among Us is that in an alternate reality, the Joker gassed Superman was a drug that made him see Lois Lane as Doomsday, whom he then proceeded to beat to death (offscreen). To make matters worse, the atomic bomb that the Joker rigged up was synced to Lois' heart rate. Once she died, the entire city of Metropolis was destroyed. This forces Superman past the Moral Event Horizon, turning the entire world into a police state where he believes Utopia Justifies the Means.
- The Suffering: Ties That Bind features a drug addict kid (suffering withdrawal) mistaking the protagonist for his father. Unlike most examples it's played for drama rather than laughs (you have the choice between letting him die or escorting him to his friend's stash).
- Monkey Island
- In Onmyōji, once Awakened, Yōkinshi can cause his enemies to become confused and whack each other using his music.
- Early in Kingdom Hearts I, after getting knocked out in a fight against Squall, Sora thinks he sees Kairi talking to him about the Heartless when he wakes up, but it's actually Yuffie.
- Phoenix Wright: Ace Attorney: The old man in the boat rental shop mistakes Phoenix and Maya for his children Keith and Meg respectfully. He asks them to take over his pasta shop (that also rents out boats). However, it turns out that he was faking his dementia the whole time.
- Near the end of Spec Ops: The Line you fight a Heavy Trooper that Walker perceives as his dead squadmate, Lugo. This only happens once per game; if you die while fighting him, the game will spawn a normal Heavy Trooper when you're revived at the last checkpoint.
- Dawn of War II: After being interred in a Dreadnought, Davian Thule mistakes Thaddeus for Gabriel Angelos, telling him "the secrets of Cyrene lie safe with me". Once he gets better used to it, he no longer gets anyone mixed up.
- In Dark Souls I, Quelaag's nameless Ill Girl sister mistakes you, the Player Character, for her, because she is continuously wrecked by a horrific disease to the point of blindness. To make matters worse, you have to have killed Quelaag to meet her sister, and the game doesn't miss a chance to rub it in.
- Diablo II: Marius, who has gone completely insane, is telling of the events that occured in the backstory of the game to a visitor, who he thinks is the Archangel Tyrael, culminating with the ruined man entrusting Tyrael with Baal's soulstone. Then he discovers that his visitor isn't Tyrael—it's none other than Baal himself.
- In the first Paramedium game, the senile Mrs Clansey ends up mistaking Nina for her daughter (whom she killed in what might have been a botched attempt to induce miscarriage) and mistaking Lance for her daughter's boyfriend (who had gotten her daughter pregnant and whom she may have killed too).
- In Girl Genius, Gil misidentifies everything for a while after being thrown against a wall by a clank and being in pain from a number of previous injuries. He spends a number of pages convinced that he's in Paris, rescuing Damsel in Distress Zola from a number of deadly traps without realising.
Gil: [to a suit of armour] Pardonnez-moi, monsieur, mais où est la catastrophe?
- In Something*Positive, an Alzheimer's-afflicted Fred mistakes PeeJee for his late wife, Faye. She plays along to give Fred one more moment with his beloved.
- In Futurama, a delirious Fry invokes this trope toward Nibbler (who's coshed him) as he comes to in the latter's spaceship.
Fry: Are you my mommy?
- The Legend of Korra: In one episode, a delirious Lin briefly imagines fifteen-year-old Suyin standing at the door talking to her. It's actually Korra.
- Mickey Mouse (2013): In "Shifting Gears", a delirious Mickey mutters "Is that you, Walt?"
- Rugrats: In "Reptar's Revenge", after Angelica takes an incredibly fast and nauseating spin on a carnival ride.
Didi: Honey, are you okay?
Angelica: I think so, Uncle Stu.
- Star Wars Rebels: In "Visions and Voices", Ezra hallucinates a rebel soldier as Maul, and nearly kills him before Kanan manages to snap him out of it.
- A rare side effect of anaesthetia is that people can sometimes have memory problems immediately after waking up. As a result of this, there's a famous online video involving a man who can't get over the fact the beautiful woman with him after his operation is the woman he married years ago.