Sanity Slippage: Western Animation
- The Christmas episode of Adventure Time shows that, centuries ago, before The End of the World as We Know It, this happened to an antique collector by the name of Simon Petrikov after he made the mistake of wearing a cursed artifact. A thousand years of sanity slippage later, the man he was is completely gone, and what remains only knows himself as The Ice King.
"But I'm losing myself and I'm afraid you're going to lose me too."
- It gets worse. Later episodes document Simon's attempts at surviving and raising Marceline after the nuclear holocaust, and his desperation at remaining himself.
- Being harassed 24/7 by the spirits in his castle (that only he can see, thanks to his wizard eyes) probably hasn't helped any, either.
- An episode of American Dad! has Stan going insane when his neighbors criticize him.
Hayley: He's right, Dad. You're going insane.Stan: Oh am I!? Would an insane man try to drink you!? (holds up Klaus to his lips and starts sucking on him)
- Animaniacs has this happen almost Once per Episode to the unfortunate soul the Warners decide to be their "special friend". Most of the time they deserve it, though.
- On a rare occasion, the Warners themselves, who usually feign insanity, will genuinely go insane when even they can't cope with the madness.
- Slappy Squirrel suffers this in "One Flew Over the Cuckoo Clock" after being forced to watch talk shows.
- Azula in the finale of Avatar: The Last Airbender. Her slippage began with Mai and Ty Lee's betrayals a couple episodes earlier. When Ozai told her to remain in the Fire Nation as Fire Lord, she became increasingly more paranoid. She acted on the paranoia, then began hallucinating, and eventually had a Villainous Breakdown.
- Aang went through one half a season previously due to sleep deprivation. He started out with just encouraging everyone to prepare for alarmingly specific things to go wrong and ended up having a several-minute hallucination of a swordfight between Momo and Appa while a six-armed Guru Pathik floated past singing about chakras.
- Harleen Quinzel, who would later become Harley Quinn, in the Batman: The Animated Series episode "Mad Love".
- Louise on Bob's Burgers was never exactly the sanest kid around, but in "Earsy Rider" she has a mental breakdown after her bunny ears are stolen. It gets even worse when she thinks they've been destroyed.
- Happens to Dog in one episode of CatDog, when he learns that meat comes from animals and becomes convinced that food are his friends.
- Jeff in the Clarence episode "Average Jeff".
- While the Red Guy from Cow and Chicken isn't exactly sane to begin with, he ends up having a complete mental breakdown in the episode "I Scream, Man" as a result of taking a job that he despises: as an ice cream man. Predictably, he ends up in a mental clinic.
Red: AAAAAHHHH!!!!! I CAN'T TAKE IT ANYMORE!!!! I don't have any ice cream! Not one, so! EVER! (Hangs near the side of the cop, then switches to a calm, quiet voice) I don't even like ice cream, (switches back to Large Ham mode) OR KIDS! It says "Eye Screem" on my truck, not "Ice Cream"! Get it? 'cause I SCREAM!!! Look at me. (screams while spinning in circles) SCREAMING IS MY HOBBYYYYYY!!!!!!.Policeman: (hits Red with a sausage) It's the padded cell for you, scream man!
- Happens all the time in Ed, Edd n Eddy:
- Eddy loses it in "Laugh Ed Laugh" when all the Kids get chicken pox, leaving him with no one to scam.
- "Little Ed Blue" has Ed become massively pissed off for apparently no reason. He had a pebble in his shoe. This revelation drove Edd and Eddy crazy too. But when Eddy slaps him in an attempt to snap him out of it, Ed goes into a unstoppable rampage, eating metal slides and nearly snapping Plank in half.
- Kevin starts going manic from paranioa when the Eds go missing in "No See Ed."
- Rolf goes ballistic when he thinks Ed has affiliated himself with wolves in "No Speak Da Ed."
- Futurama: Fry suffers this in "Insane in the Mainframe" as a result of being a human confined to a robot asylum.
Amy: You've gone from crazy like a fox to crazy like Fox News.
- In "Mobius Dick", Leela went insane when she became obsessed with trying to kill a space whale as revenge.
- If you look closely at some of the text in Journal 3 on Gravity Falls, it seems like the Author underwent something like this.
- Mabel slowly starts losing it in the season 1 episode "The Time Traveler's Pig" after Dipper's time travel antics cause her to lose her pet pig. After handing out calculators to people across eight centuries, she eventually breaks completely and starts banging her head against a post and doesn't stop for a month, during which time she grows vines and gets a shoulder snail. Fortunately, it's temporary, and getting her pig back seems to resolve all the problems, but this example is played more for drama than laughs, despite its absurdity.
- Old Man McGucket helped build the machine in Stan's basement thirty years ago, but an accident with the device heavily traumatized him. He then built a gun that would erase the memory from his mind, creating the Society of the Blind Eye so that others wouldn't be freaked out or traumatized by the weirdness of Gravity Falls. However, repeated use of the memory wipe took a toll on McGucket's sanity, until he was reduced to the junkyard dwelling town kook he is today.
- Dib of Invader Zim isn't that stable to begin with (being one of the handful of reasonably intelligent people in a Crapsack World full of idiots will do that), but over the course of the series becomes increasingly desperate, paranoid, and manic, and talks to himself with greater frequency.
- Though Justin Hammer already was a Rich in Dollars, Poor in Sense Psychotic Manchild from the start in Iron Man: Armored Adventures, he gradually loses the little sanity he has left over the course of the series.
- Played for Laughs on Jimmy Two-Shoes, when Jimmy is left the only person in Miseryville awake while everyone else is in hibernation. He slowly begins to go crazy.
- Hank's barber Jack in King of the Hill started going senile, culminating in Bill mentioning something about Jack getting in a high speed police chase. Earlier we'd seen him saying he couldn't give Hank a haircut because he didn't have a stapler, spraying Hank's hair with peroxide before walking out of his shop and assaulting someone for their bicycle, and finally dumping shaving cream on his head and removing it with a hair dryer.
- This is oddly reversed a few seasons later when Luanne starts working at Jack's shop and he's got all his cognitive abilities working in okay condition, implying the above was either a nervous breakdown, he'd been put on very strong medication, or bad writing.
- In the episode "Pretty, Pretty Dresses" Bill is very lonely and depressed, and finally loses it when Hank destroys the gifts he'd been saving for his ex-wife Lenore in case she ever came back. He starts wearing her old clothes she'd left behind and talks in a falsetto voice, believing that he himself is Lenore; eventually Hank is able to break him out of it and gets him to get over Lenore.
- Looney Tunes: Daffy Duck seems to fall victim to this a lot. A perfect example occurs in Duck! Rabbit! Duck! after he gets shot by Elmer Fudd one too many times:
Daffy: (hysterical) Shoot me again! I enjoy it! I love the smell of burnt feathers! And gunpowder! And cordite! I'm an elk — shoot me! Go on, it's elk season! I'm a fiddler crab — why don't you shoot me?! It's fiddler crab season!
You know what this'll cost you? Thirty days...hath September, April, June and Montana! All the rest has cold weather! Except in the summer!
- Happy Rabbit (the beta Bugs Bunny) in "Hare-Um Scare-Um" does a song that tells how watching Looney Tunes cartoons drove him insane. Imitating a police officer, his throwing the book at John Sourpuss' dog tells all.
- A year earlier, Daffy Duck himself tells how he did quite well working on a merry-go-round until it broke down.
- In The Looney Tunes Show not only Daffy, but everybody is liable to get bonkers (after all, it's a mostly Crapsaccharine World/ Stepford Suburbia full of Cloudcuckoolanders). As an example, Porky has turned from an apparently wealthy Jerk Jock in high school to a middle-class burn-out prone to suffer this so frequently that it gets in Black Comedy and even "Dude, Not Funny!" territory; and Bugs didn't act like himself after he started consuming "Spargle" (being Played for Laughs).
- Mickey Mouse in the short "New York Weenie" and "Dog Show".
- My Little Pony: Friendship Is Magic: The Fan Nickname for this is "Cutie Mark Failure Insanity Syndrome", given that a pony failing to live up to their special talent (symbolized by their cutie mark) is the most common cause of ponies going nuts. (It's worth pointing out that in all of these cases, the insanity was cleared up by the end of the episode with The Power of Friendship.)
- In "Party of One", Pinkie Pie thinks her friends are avoiding her because they're sick of her parties. Her normally curly hair goes straight, she makes her own party guests out of things like a sack of flour and a pile of rocks (whom she holds conversations with), her colourful persona becomes noticeably darker, as if it's under a shadow, and the normally insufferably cheerful pony becomes cranky, miserable, and borderline paranoid schizophrenic, all the while sporting a Slasher Smile. Her slippage even comes complete with Creepy Circus Music (which has a disturbing resemblance to the leitmotif of a certain personification of chaos).
- In "The Best Night Ever", Fluttershy snaps at the Grand Galloping Gala due to all of the animals running in fear from her. After her increasingly desperate methods fail, she goes into full blown Yandere mode, unleashing animal-based chaos with the line "You're... going to LOVE MEEEE!".
- In "The Return Of Harmony Part 1" and "Part 2", the discorded mane ponies' misbehavior becomes worse as the episode progresses.
- Twilight Sparkle goes through a complete psychotic break in "Lesson Zero". Convinced that she's about to fail her duty to Princess Celestia, her mane goes disheveled, her teeth grind, her eyes become unfocused, she talks to herself, and she starts teleporting at random while undergoing a complete nervous breakdown. It culminates in an (unintended) mass hypnosis of Ponyville that requires the Princess herself to intervene, furious at her student for abusing her powers.
- Keep in mind that all those examples happened in five consecutive episodes.
- In "Putting Your Hoof Down", Fluttershy's takes some assertiveness training which works a little too well, resulting in her taking multiple levels in Jerkass and becoming increasingly violent, paranoid and aggressive to the point that she reduces Pinkie and Rarity to tears.
- Twilight goes crazy again in "It's About Time" due to a warning from her future self that got cut off before the important bit could be delivered, leading to a spiral down into the depths of paranoia.
- Princess Luna experiences this a thousand years before the time of the series. Literally consumed with jealousy and anger towards the ponies rejecting her beautiful night in favour of Celestia's day, she transforms into Nightmare Moon and tries to enact eternal night in a stubborn attempt to force the ponies to love her, showing that even a Physical Goddess isn't immune to CMFIS. In "Luna Eclipsed" she runs the risk of having to bear these insecurities all over again when the ponies begin to reject her once more, but fortunately Twilight is there to help.
- Before "Games Ponies Play" aired, people were expecting another "Twilight goes crazy" episode. They were likely surprised when this trope was averted for that episode because Cadance taught her a controlled breathing excercise to relieve stress.
- But if her hyperventilating near the climax of the episode is anything to judge by, it was a pretty near miss.
- Rarity suffers from this in "Simple Ways" after swapping roles with Applejack, and has a complete breakdown in the Bad Future Nightmare Sequence from "For Whom The Sweetie Belle Toils".
- In Inspiration Manifestation, the more Rarity uses the eponymous book's power, the more deranged she becomes.
- Rainbow Dash's turn comes in Tanks For The Memories, where her anxiety at having her beloved tortoise hibernate for the winter drives her to try and stop winter from happening.
- In The Lion King 1 1/2, during a scene approximately taking place during Scar's Villain Song in the original movie, Timon is on the verge of cracking in his "dream home" quest...
Timon: (comes across a steam vent) Hey! This is home sweet home, baby! Home— (gets sent into the air a bit by the eruption) Ha ha! Steam! Ha ha! Steam is good. Steam is—is—is water. Whoo! Gotta have water. You know, for the dream home. Steam home, dream home! Steam, steam, steam.
- Ren of The Ren & Stimpy Show frequently falls into this. Stimpy sometimes does too. And boy is it creepy.
- Candace from Phineas and Ferb. It's not gradual and it's not regular like most examples, but it's definitely there. Seriously, this girl needs help. She has a psychological need to bust, it's shown at least twice that she can't go without it. That doesn't smack of good mental health...
- If it wasn't clear before, the episode "Monster From ID", which takes place largely in Candace's subconsciousness, seals it. Candace's head is one messed up place.
- Pinky and the Brain: Snowball in "Welcome to the Jungle", where he's the leader of makeshift jungle tribe made up of tourists and it's implied he's been hallucinating.
- Rigby of Regular Show goes cuckoo when he learns the "Death Punch of Death", to the point where he's willing to drown in lava if it means beating Mordecai at Punchie's.
- Rugrats: From the movie, Tommy totally snaps and almost pours mashed bananas on Dil, knowing the monkeys will be attracted to it. It's thundering and raining the whole time, and Tommy just starts acting more and more crazy as he starts ranting about how much Dil has ruined his life.
- In ''Chuckie's Wonderful Life", Chaz goes insane in a world without his son.
- Stu also loses it when he's forced to take care of Angelica after she pretends to have broken her leg.
- South Park:
- "1%" ends with the implication that Cartman's sociopathic tendencies are growing into a full blown psychosis.
- Even without any greater implications, you can see his sanity suffer with each stuffed animal destroyed.
- Randy in "A Nightmare on Face Time". Complete with a shot-for-shot, line-for-line homage to Jack Nicholson and The Shining.
- "1%" ends with the implication that Cartman's sociopathic tendencies are growing into a full blown psychosis.
- SpongeBob SquarePants and Mr. Krabs try to keep their sanity when they believed they killed the health inspector. Turns out that the inspector is still alive, and the Krusty Krab passes inspection.
- In "Pickles", SpongeBob's life takes a turn for the chaotic after a Jerk Ass customer claims that he forgot the titular condiment. By which we mean he tries to cook his bicycle and hangs the toaster on his front door.
- Poor Squidward. In between being the entire ocean's Butt Monkey and victim to the constant shenanigans of his next door neighbors, SpongeBob and Patrick, it's no wonder he's been shown to break down into a sobbing wreck or fits of maniacal laughter when the Amusing Injuries and ever-present failures prove too much to handle. In "Squid's Day Off" Squidward tricks SpongeBob into running the Krusty Krab all by himself while he takes a day off, but he keeps imagining SpongeBob destroying the Krusty Krab and repeatedly goes back and forth to and from his house. While taking a bath he hallucinates SpongeBob is watching him and runs off to the Krusty Krab wearing only bubbles.
- SpongeBob frequently has Sanity Slippage to the point that you wonder whether he's exactly sane to begin with...
(from "Stuck in the Wringer")
Patrick: Hey, whatcha watchin'?
SpongeBob: (watching static on TV) My favorite show. (the TV dies) Ha, ha, I love that part!
- Mr. Krabs goes crazy when the squeaky noise of the rubber boots he gave Spongebob becomes too much to bear.
- In "Clams" after Mr. Krabs loses his millionth dollar we see him slowly go completely insane. The cut back to Mr. Krabs, who begins giggling maniacally and tears his two eyes out, using them as a jumprope is genuinely disturbing.
- When Spongebob decides to live with the jellyfish in "Nature Pants," Patrick, who wasn't all there in the first place, goes ballistic, planning on catching Spongebob and keeping him in a jar.
- Kowalski gets this a lot in The Penguins of Madagascar.
- The Simpsons episode "Springfield Up" contains a very swift summary of how doctor/lawyer Eleanor Abernathy went off her rocker and became the town's yowling cat lady.
- Frank Grimes learns the hard way in "Homer's Enemy" that being the Only Sane Man in a Crapsack World is not conducive to one's long term health.
- Homer himself does so in The Shinning segment of "Treehouse of Horror V" when the cable stops working and they run out of beer, all thanks to Mr. Burns.
Homer: No TV and no beer make Homer something something...
Marge: "Go crazy?"
Homer: Don't mind if I do!! (proceeds to go crazy)
- Toy Story. Buzz really doesn't take realizing he's a toy well.
Buzz Lightyear: YOU SEE THE HAT?! I AM MRS... NESBITT! (laughs maniacally)
- Transformers Prime showcases Megatron's slow descent into (further) homicidal madness. Doping using the blood of Unicron certainly hasn't helped, but he's clearly slipping even without it. It becomes most clear when he get the Dark Star Saber, whereupon he starts shouting about how he'll tear this world apart (despite the fact that doing that dooms the entire universe).
- More or less the plot of Wakfu's Start of Darkness prequel episode.
- Steven Universe: In the non-canon Uncle Grandpa crossover episode, Pearl, who is the logical (most of the time), brainy perfectionist of the team, becomes increasingly unhinged and suffers at least three mental breakdowns from dealing with Uncle Grandpa's weirdness. This is even emphasized by a significant downgrade in her appearance and animation and major scenery chewing by her voice actress. It overlaps with temporary Flanderization because while Pearl is susceptible to bouts of hysterics and irrational behavior, she's never lost it to this degree before or since.
- In Chille Tid it is implied to have happened to Jasper after she is trapped in Malachite by Lapis, when she sees Steven again, crawling towards Steven with an insane look on her face and a tone in which she sounds like she plans on eating him alive.
- On Western Animation/Stanley, Elsie experiences one when she grows tired of waiting for the butterfly to emerge from its chrysalis in "Caterpillar Countdown." The longer the wait, the worse she gets, as she really wants to see that butterfly.