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[[quoteright:317:[[Webcomic/GunnerkriggCourt http://static.tvtropes.org/pmwiki/pub/images/Jack_slipping_4748.jpg]]]]
[[caption-width-right:317:Get some sleep, Jack.]]

->''"Because madness, as you know, is like gravity. All it takes is a little '''push'''!" ([[LaughingMad Laughs maniacally]])''
-->-- '''SelfDemonstrating/TheJoker''', ''Film/TheDarkKnight''

A character has been a bit ... off for a while now. Maybe they just [[NotHimself haven't been themselves]], maybe they've gone as far as painting a RoomFullOfCrazy while reciting a MadnessMantra, or maybe they've gone through a MadnessMakeover, but it's apparent from their actions that their rational mind is losing its grip and they are sliding inch by inch toward insanity.

The end result of this varies, depending on the tone of the series and who the character is. If the series is [[DarkerAndEdgier dark and edgy]], they may go on a [[UnstoppableRage murderous rampage.]] On the other hand, if it's [[LighterAndSofter light and soft]], it may just be PlayedForLaughs, becoming a source for their hilarious dialogue and wacky plans. A villain is likely to have a VillainousBreakdown resulting in KarmicDeath, while a hero will just have a HeroicBSOD and then get better.

Occasionally, a character will be seen [[ReluctantPsycho holding back their insanity and generally keeping it in check]], until that final straw breaks the camel's back and they finally snap, having a massive FreakOut.

And most rarely, the Sanity Slippage is the effect of an InsanityPloy on a victim ''by'' the Villain.

A SuperTrope to SanitySlippageSong.

Compare GoMadFromTheRevelation, FreakOut, VillainousBreakdown, RoomFullOfCrazy, MadnessMantra, LaughingMad, and WithGreatPowerComesGreatInsanity.

[[noreallife]]
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!!Examples:
[[index]]
* SanitySlippage/AnimeAndManga
* SanitySlippage/{{Film}}
* SanitySlippage/{{Literature}}
* SanitySlippage/LiveActionTV
* SanitySlippage/VideoGames
* SanitySlippage/WebOriginal
* SanitySlippage/WesternAnimation
[[/index]]

[[foldercontrol]]

[[folder:Comic Books]]
* ''Comicbook/TheKillingJoke'' is one take on the Sanity Slippage that eventually led to the origin of SelfDemonstrating/TheJoker. But the Joker admits he's an UnreliableNarrator and could be remembering wrong or making the whole thing up. He attempts something similar to crack [[spoiler:Commissioner Gordon. He doesn't succeed.]]
* Rorschach from ''Comicbook/{{Watchmen}}'' is clearly mentally unstable even before the event that causes him to [[JumpingOffTheSlipperySlope slide off of the slippery slope]].
* Jackson Georges from ''Comicbook/ExMachina'', Mayor Hundred's former NSA handler fits this trope. In flashbacks the reader is shown how the cryptic shard that Mitchell found when he got his powers slowly drives Jackson to levels of extreme paranoia. He develops an unfounded contempt for Mitchell, claiming that without Mitchell's appearance and the mystery of the shard, he could have foreseen and prevented 9/11. He becomes obsessed with protecting his family from dirty bombs and the like, buying a HazmatSuit and making tally marks on the wall to represent god knows what. It's clear he's a step away from the deep end. Darkly subverted when [[spoiler:in desperation to save their failing marriage, his wife breaks into his work shed and steals the shard. A few seconds near a TV are enough to drive her completely and utterly insane, leading her to kill her daughter, husband, and dog. She even chops off her own arm with the shard itself. It was an incredibly jarring and brutal twist on the slow burn of paranoia the reader had been witnessing for months.]]
* J. Jonah Jameson from ''ComicBook/SpiderMan'' suffered a nervous breakdown late in Marv Wolfman's run, to the point where he believed Spider-Man was stalking him. However, Wolfman left the book before long, and Roger Stern {{retcon}}ned the whole thing away as mind-control.
* [[Comicbook/{{Azrael}} Jean-Paul Valley's]] stint as Franchise/{{Batman}} during the "Knightquest" portion of the ''ComicBook/{{Knightfall}}'' storyline was this. After being doused with the Scarecrow's Fear Gas, the hypnotic trance known as The System kicked in, haunting Jean-Paul with images of his father and of Saint Dumas, the "creator" of the order he once was part of. As he's haunted by these apparitions, The System drives him to be more brutal and continuously modify the Bat-Costume, the pinnacle being when he allowed Abbatoir to die, condemning his captive to death, modifying the Bat-Costume to the point where it was less Batman and more Azrael and outright alienating Robin, Commissioner Gordon, and ''Bruce Wayne'' and deciding that all criminals need to be put out of their misery. It's at that point that Bruce decides enough is enough and sets out to take back the Mantle of the Bat.
[[/folder]]

[[folder:Fan Works]]
* Jack O'Lantern, the ArchEnemy of [[FanFic/UltimateSpiderWoman Spider-Woman]], commits increasingly violent and destructive crimes as the series progresses. He goes from robbing banks to taking people hostage to going on killing sprees to orchestrating a bloody city-wide MobWar. Even in jail, we see him fantasizing about carving up human heads the way people do Halloween pumpkins. What's unusual is that Jack always had these sadistic urges-the Sanity Slippage comes from the escalating nature of his crimes.
* [[Manga/AxisPowersHetalia Austria/Roderich Edelstein]] in the ''NineteenEightyThreeDoomsdayStories'' is portrayed for the most part as undergoing through this. His obsession in finding out [[HopeSpot whether Hungary survived]] [[WorldWarIII Doomsday]] grows increasingly desperate (and irrepressible) over time to the point that others eventually start wondering if he's gone delusional from grief. [[spoiler:He doesn't.]] It's also mentioned to have happened as well with Romano (hijacked by TheMafia as his brother's successor) and Poland (having his personality shattered).
* Calvin goes a ''little'' crazy trying to watch a pug in ''Fanfic/CalvinAndHobbesTheSeries''.
* In the vein of the [[WesternAnimation/MyLittlePonyFriendshipIsMagic Cutie Mark Failure Insanity Syndrome]] described below, ''[[http://www.fimfiction.net/story/24890/the-audience The Audience]]'' by Reality Check states that Trixie herself is diving into one as her special talent isn't magic like most unicorns, but rather stage magic, illusions and theatrical personalities. The constant heckling, jeers and challenges towards her achievements that she was receiving were making her the JerkAss that she was portrayed as in canon.
* Fanfic/TotalDramaStranded: Briony gets a major one very quickly when [[{{Jerkass}} Calvin]] begins relentlessly bullying her.
* From the sister story, Fanfic/TotalDramaSwitcheroo, Missy gets an even bigger one.
[[/folder]]

[[folder:Music]]
* Songs about going insane are quite common, actually. Many examples at SanitySlippageSong.
* "Stan" by Music/{{Eminem}} shows the story of a fanboy with a seriously screwed-up life and a downward spiraling sanity. The video starts with Stan bleaching his hair just like Eminem's, then Stan starts writing letters to him every so often in his room all plastered with posters of Eminem, then he sends Eminem a ''really pissed off'' letter complaining about how he missed Stan and his brother at a gig. When his pregnant girlfriend scolds him for wasting his day on watching Eminem, that's the final straw on the back, and he ends up tearing all his posters, tying his girlfriend in his car's trunk, and driving off a bridge.
** Then Eminem sends back a letter, and starts by apologizing for how long it's taken him to finally respond. Trippin'. Best part: In his response letter, Eminem decides to cite a story he heard on the news about a guy who drove his car off a bridge with his pregnant girlfriend in the trunk, in the hopes that it'll get Stan to calm down a bit. Then Eminem realizes ''the news story was about Stan''. "Damn," indeed.
* The Music/NineInchNails album ''The Downward Spiral'' is a ConceptAlbum that's about ExactlyWhatItSaysOnTheTin: the gradual destruction of an unnamed man, from the beginning, to [[spoiler:his suicide]].
* The Violent Femmes' "Country Death Song" is pure American Gothic: rural guy goes mad from isolation and boredom, [[spoiler: throws his little daughter down a well]], then broods over his guilt till...you can probably imagine.
* Music/PinkFloyd's ''Music/TheWall'' chronicles a man slowly alienating himself from the world, causing his mind to collapse on itself until finally what's left of his sanity stages an intervention and forces him to actually ''deal'' with his problems.
** The band's previous albums, ''Music/TheDarkSideOfTheMoon'' and (especially) ''Wish You Were Here'', were inspired by the real-life sanity slippage of former bandleader Syd Barrett, who had become impossible to work with. "''Now there's a look in your eyes / like black holes in the sky''". His former bandmates reluctantly dropped him and felt guilty about it ever after. The two albums were enormously successful, but the subsequent non-stop grind of touring to unappreciative audiences caused Roger Waters to suffer a sanity slippage of his own, which directly inspired ''The Wall''. Which was an even more enormous success!
* By Music/CoheedAndCambria's third album, the author in the frame story of their sci-fi epic has started talking to a bicycle and making both death threats and declarations of love to the ex-lover for whom he wrote the story. In the previous albums the author was not a significant character, and the only real sign of his instability was the fact he was writing the kind of material you can make a Prog Rock ConceptAlbum out of.
* ''Music/{{Gorillaz}}'': Both Murdoc and [[TheWoobie 2D]] show signs of this as of phase 3, rambling and gibbering like never before. 2D seems a bit sharper than earlier chapters, though, while Murdoc's just gotten bolder and more malevolent.
[[/folder]]

[[folder:Professional Wrestling]]
* [[Wrestling/RonKillings R-Truth]] turned heel after losing out on a WWE Championship opportunity. And after that, his mind.
* [[Wrestling/BryanDanielson Daniel Bryan]]. Yes! Yes! Yes! Yes! Yes! And after Wrestling/AJLee left him at the altar, it turned into: No! No! No! No! No!
* In 2010, poor Wrestling/ShawnMichaels started losing his mind after not being able to beat Wrestling/TheUndertaker at Wrestling/WrestleMania XXV. And after Wrestling/WrestleMania XXVI, his career. He regained his sanity at this point.
[[/folder]]

[[folder:Tabletop Games]]
* A daily occurrence in ''TabletopGame/{{Warhammer}}'' and ''TabletopGame/{{Warhammer 40000}}''; living in an endlessly terrible CrapsackWorld will do that. Witches/psykers are especially vulnerable to Slippage, thanks to the source of their powers being the home of TheLegionsOfHell.
* Also appears in WarhammerFantasyRoleplay, it has a mechanic for going insane and lists quite a nice amount of mental illnesses for which your character can suffer
** As befits its source material, GaidenGame ''TabletopGame/DarkHeresy'' has mechanics by which players can go insane.
* ''TabletopGame/CallOfCthulhu'' is famous for introducing the SAN attribute, which drops a little each time the players encounter a monster or cast a spell, or something.
* Everyone in ''TabletopGame/NewWorldOfDarkness'', from normal humans to blood-hungry vampires to reality-bending mages, has a KarmaMeter. As you slide down the slippery slope, you tend to become a little more unstable with each step, until finally, humans are reduced to raving lunatics, vampires and werewolves go nuts and become meat-hungry animals, mages and changelings fly off the deep end and lose the ability to separate reality from fantasy, and prometheans lose hope of ever becoming humans.
* The ''TabletopGame/OldWorldOfDarkness'' also has sanity-slipping {{Karma Meter}}s, though not all splats have them.
* The fan-made ''World of Darkness'' game ''TabletopGame/GeniusTheTransgression'' is unique in that players start out insane by nature of their [[MadScientist profession]], and as they lose Obligation start unconsciously [[RealityWarper altering reality]] to fit their delusions.
* ''TabletopGame/{{Exalted}}'' loves this trope:
** The Solars gradually experience this as they become more and more godlike, from both the Great Curse and general detachment from humanity and less powerful divine beings.
** Being close to a Primordial War survivor in the First Age can be dangerous, humiliating, and bad for your physical, mental, and social health.
** Also happens to Infernals. They have access to Yozi Charms. Everything the Yozis are, is made of Charms. Most of the Yozis are insane, and their Charmsets tend to be arranged so that the good stuff with no drawbacks is padlocked by something with benefits that makes you a little crazier. The best example of this is Kimbery, who has an entire Charm tree (built on ThePowerOfHate) locked behind something that permanently skews the sanity of its user to be either more naive or more vindictive, depending on the chosen variant.
* In ''TabletopGame/FadingSuns'', Psychics and Theurgists are prone to "Urge" and "Hubris" respectively.
* Characters in ''TabletopGame/EclipsePhase'' are very hard to [[DeathIsCheap kill permanently]] due to [[BrainUploading cortical stacks and backups]], fortunately for [[KillerDM GMs]] there's a mechanic called "stress points" that can cause psychological disorders or permanent catatonia if the PC lets them accumulate.
* Any KillerGameMaster worth the title can put this into ''any'' game.
[[/folder]]

[[folder:Theater]]
* Blanche in ''Theatre/AStreetcarNamedDesire'' as well as the film adaption with VivienLeigh.
* ''Theatre/SweeneyToddTheDemonBarberOfFleetStreet'' does this with its eponymous character via [[SanitySlippageSong "Epiphany"]].
* The title characters in ''Creator/WilliamShakespeare'''s ''Theatre/{{Macbeth}}'' and arguably ''Theatre/{{Hamlet}}''.
* The title character of ''ThePhantomOfTheOpera'', though your mileage may vary on how sane he was to begin with. But he's definitely completely off the beam by the end, determined to have Christine at all costs, even if he has to blackmail her into marriage by threatening to kill her lover.
[[/folder]]

[[folder:Web Comics]]
* Jack from ''Webcomic/GunnerkriggCourt''. He started off as a pretty normal guy, then he briefly got pulled into a DarkWorld and saw some ''very'' unpleasant things. Since then he became increasingly antisocial, paranoid (at one point he starves himself because he's convinced the Court has laced his food with nanobots to track him) and amoral (compare his treatment of the Laser Cows to his treatment of the Guard Robot). [[http://static.tvtropes.org/pmwiki/pub/images/Jack_Progress_7447.jpg Heck, even his appearance became worse over time.]] Fortunately, now that [[spoiler:the whitelegs is out of his head,]] he's gotten almost back to normal. Oh, and [[spoiler:[[TheCuckoolanderWasRight he was right]] [[ProperlyParanoid about the food]].]]
* Vaarsuvius spent most of "Don't Split The Party" undergoing this in ''Webcomic/TheOrderOfTheStick''. [[spoiler: They ultimately recovered.]]
* Jin of ''Webcomic/WapsiSquare'' suffers from a bad case of this after [[spoiler:destroying the calendar machine. It was actually built at least partially for the purpose of keeping her sane.]]
* ''Webcomic/{{Homestuck}}''--
** Karkat starts getting shades of this after a particularly brutal TraumaCongaLine. [[spoiler: Two of his friends were murdered in from of his eyes, two others are on killing sprees, he's dragging his newly-blinded friend's body (and accidentally drops him down some [[RunningGag stairs]], and he gets a message from his girlfriend, pronouncing the details of another murder - and when he tries to contact her, one of the AxCrazy trolls responds, hinting that she's been killed.]]
--> There. Good as new, best friend! It's like it never happened. No one can ever blame you for dropping him down the stairs now. Stairs? What stairs! Ha ha ha!
** And now Rose is showing signs of it too, now that [[spoiler: her mother's died.]]
--> "This is because, as is [[CallBack now painfully obvious to anyone with a brain]], you have basically [[spoiler:gone completely off the deep end in every way. You have officially gone grimdark.]]"
* ''Webcomic/GarfieldMinusGarfield'': With no cat to give him sarcastic remarks, Jon Arbuckle slowly descends into madness. Examples include [[http://garfieldminusgarfield.net/post/27473059 smushing ice cream cones into his face]], [[http://garfieldminusgarfield.net/post/40406640 dressing up for a date... that's in three weeks]], ''[[http://garfieldminusgarfield.net/post/78032638 jumping in the streets wearing a party hat]]'', [[http://garfieldminusgarfield.net/post/81381173 chasing cars in the manner of dogs]], [[http://garfieldminusgarfield.net/post/503880743/try-g-g-in-book-form breaking]] [[http://garfieldminusgarfield.net/post/26654167 down]] sobbing at the most random times, [[http://garfieldminusgarfield.net/post/30759171 Madness Speak]], and, finally, [[http://garfieldminusgarfield.net/post/69159474 being sent to a Mental Hospital]].
* ''Webcomic/BittersweetCandyBowl'' has Lucy having a mental breakdown when Michael falls off a rock bridge while saving her.
[[/folder]]
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