Personal Horror

"It's your sense of alienation from self that provides, perhaps, the deepest terror. Where other meters measure how traumatized you are by the things that happen to you, Self measures how traumatized you are by your own reactions to those things. To put it another way, the only thing you can ever really be 100% sure of is 'I think, therefore I am.' The Self meter measures how uncertain you are about the 'I' in that statement."

— Unknown Armies corebook.

This trope is when a painful betrayal of one's self image, self-loathing, internal conflict, personal failing/flaw or guilt is Played for Drama. It can be because of what someone did, didn't do, tried and failed to do, or they were just unlucky and got caught up in a bad situation. The key part of this trope is that something goes against the character's personal moral code, leading to the alienation of self.

Can lead to Heel–Face Turn or the character becoming The Atoner. Sometimes results in Past Experience Nightmares or the character crossing the Despair Event Horizon. Some characters have an overlap with You Are What You Hate. Often results in Heroic BSoD, sometimes after running Heroic Safe Mode.

Because this trope is personal, examples will be of a different kind for different characters. When editing, keep in mind to explain why an example is this trope for that character.

Can cover:

Accomplice by Inaction: You didn't do something, and now you feel guilty about it.
And I Must Scream: Being alive and aware for very, very long, but you can't do anything.
Became Their Own Antithesis: You became what you used to hate.
Brainwashed and Crazy: Being horrified by what you've done while under mind control.
Cold Equation: Almost out of supplies? Have fun deciding who gets to live.
Dead All Along: You find out that you or someone else was dead without being aware of it.
Forced into Evil: You were forced to do something evil.

Gollum Made Me Do It: Your other personality did it.
Heel Realization: You realize you're the bad guy.
Human Alien Discovery: You discover you aren't human, but a Human Alien.
I Let Gwen Stacy Die: You blame yourself for being unable to save a loved one.
I Should Have Been Better: You feel guilty about not doing enough/not doing everything.
The Killer in Me: Especially the amnesiac variant.
Loss of Identity: You lose what makes you you.
Loss of Inhibitions: You lose your restraint and you feel horrified and regretful of the things you've done without it.
The Mind Is a Plaything of the Body: Shapeshifting changes your personality.
Moment of Weakness: A temporary lapse in judgment causes you to make a mistake with disastrous consequences.
My God, What Have I Done?: You feel remorseful of something you've done after realizing how malicious your action was.
My Greatest Failure: You're motivated by an unfortunate mistake you made in the past.
Organ Autonomy: Your body betrays you.
Powerful and Helpless: All of those powers you rely on and you can't do anything.
Restricted Rescue Operation: Outside forces restrict how much you can do to help.
Sadistic Choice: If forced to choose between different things that betray your sense of self. Especially if taking a third option is not available or possible.
Shoot the Dog: You're forced to go against your or society's moral code in order to do the right thing.
Tomato in the Mirror: You're not who you thought you were.
Trapped in the Past: Your legal identity and everyone that knows you won't exist for decades.
What Have I Become?: You no longer recognize yourself in a new form.

Works with their own subpage:

Babylon 5

Examples:

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Anime and Manga

Neon Genesis Evangelion: all the main cast, but Shinji Ikari might be the poster boy for this trope. A person with very high moral standards, but a weak and tender heart that cannot shoulder them against the odds. He develops a bad case of self-loathing, reaching a Despair Event Horizon after the final angel and a Moral Event Horizon for himself after Dude, She's Like, in a Coma!.
Perfect Blue, along with a healthy dose of Psychological Horror and Surreal Horror. Yay, loss of identity and emotional insecurity!
Sankarea: Rea has this when she starts to succumb to her zombie nature.
Tengen Toppa Gurren Lagann: happens to the Spiral King in the prologue/parallel works.
Inuyasha goes through this after his evil side takes over.
- Kohaku realizing that he was Brainwashed and Crazy and killed his family.

Comic Books

The origin of Spider-Man involves this, as Uncle Ben's death is indirectly caused by Peter's irresponsibility.

Film — Animation

The Last Unicorn starts losing her sense of self when she's transformed into a human.
In Frozen Elsa freezes her sister Anna while trying to drive her away to protect her.
Toothless in How to Train Your Dragon 2 after being Brainwashed and Crazy and killing Stoick.
In The Hunchback of Notre Dame Quasimodo inadvertently leads Frollo to The Court of Miracles when he goes there to warn everyone that Frollo is coming.
In Brother Bear Kenai is first transformed into a bear. Then he finds out that the bear he killed earlier was Koda's mother.
In Zootopia, Judy Hopps' self-esteem takes a big hit when her own unconscious prejudices cause her to inadvertently start a speciesist panic against predators and betray Nick Wilde's trust, leading to their Plot-Mandated Friendship Failure. Her guilt over what happens is so strong that she resigns from the ZPD for a while because she feels she betrayed her own ideals.

Film — Live Action

Taxi Driver is all about the protagonist projecting his self-loathing on others, where his antagonists are just placeholders for the things he hates about himself or wants for himself.
In The Film of the Book of 1408, the overall schtick of the titular hotel room seems to be dragging guests kicking and screaming through the darkest corners of their own subconscious and beating them over the head with their own doubts, fears, and regrets. Mike Enslin discovers this to his extreme detriment.
Inception deals with the aftermath of this. In The Reveal we find out that Cobb planted the idea that her reality isn't real in his wife's head when they were stuck in a dream. This resulted in her suicide to wake up. It's unclear if she died or woke up.
In Iron Sky Renate has a Heel Realization followed by a Heel–Face Turn when she finds out who the Nazis were.
In Red Rover Kylie killed her mother with her powers, and all of Kylie's problems and life events since then have revolved around her denial of what she is. The film ends with her acceptance and owning of her powers.
In Sarah's Key the eponymous Sarah had to live with the fact she inadvertently locked his brother in the closet during the Nazi raid, he died there because she couldn't manage to rescue him and eventually her depression lead her to commit suicide as an adult.
In Fantastic Beasts: The Crimes of Grindelwald Leta Lestrange is dealing with this after swapping her brother for a baby that wasn't crying so she could get some sleep. The ship sunk directly afterward and her brother died.
Ghost Stories (2017) begins as a fairly unique but still pretty standard movie about a noted professor and skeptic being challenged to explain three cases that have haunted his mentor for years. It ends as a movie about a man suffering from locked-in syndrome, doomed to live in the world of dreams created by his own brain as a coping mechanism over the choices he's made in life.
Elise in Insidious discovers that despite her life's goal being to help people who are afflicted with supernatural entities, she unknowingly let a woman in her house die as a teenager because she believed her to be a spirit and didn't save her from being murdered by her father.

Literature

This is what the horror of Room 101 in 1984 is all about. Using your greatest fears to get you to betray the most important thing about yourself, to destroy your self-image by making you betray everything and anything that's left of what you valued before they arrested you.
The title character in Eden Green is a rationalist young woman infected with an alien needle symbiote that gradually takes over her body. Her intelligence is her main weapon, and her greatest fear is losing it to the symbiote's survival-obsessed instincts.
The Imperius Curse in Harry Potter can result in this. Both times when Voldemort took over many people were being mind controlled by him.
Funny Business is entirely about the guilt the main character feels as a result of misusing her Reality Warper powers.

Live-Action TV

In the Game of Thrones episode "Hardhome", Jon Snow, the rest of the Night Watch, and surviving Wildlings can only watch as the army of the dead grows by the almost 100,000 Wildlings they went to save.
In the Star Trek: The Next Generation episode "Best of Both Worlds", Federation Captain Jean-Luc Picard is forcibly assimilated into the Borg Collective. The trauma this caused him is explored over the course of several later episodes, the movie Star Trek: First Contact, and the later series Star Trek: Picard.

Roleplay

After fatally wounding Devin and Daigo in Dawn of a New Age: Oldport Blues Harriet is horrified to discover that she feels nothing about trying to kill them. She questions whether she's an Empty Shell, which causes her to experience severe cognitive dissonance.

Tabletop Games

The Bond and Sanity mechanics in Delta Green bring this, as Agents will start slowly burning their sanity and becoming stressed as they lose relations with the external world and isolate themselves from friends and family as their lives fall apart.
Done in both the Old World of Darkness and the new one, especially the Vampire gamelines.
Unknown Armies has the Self madness meter, which is meant to address this trope specifically.

Video Games

Honkai Impact 3rd: The protagonist Kiana has several cases of this, from her Guilt Complex over having her closest people get hurt while trying to help her and her not being able to do anything about it, to realizing that she's a "monster" or a "time bomb" due to her Superpowered Evil Side, in which she was controlled to hurt her closest ones. It's "horror" enough for her that she keeps getting nightmares about it. Her whole struggle is about how she could become a "hero that saves the world" despite suffering from all of the above.
Several characters in Pokémon Super Mystery Dungeon end up with this trope. Nuzleaf, Yveltal and Beheeyem are all controlled by the Dark Matter to turn everyone into stone and go into self-imposed exile after breaking free and helping to defeat Dark Matter.

Western Animation

Justice League does this to several of the heroes in the episode "Only A Dream". Superman's nightmare has him dealing with Power Incontinence. His heat vision kills Lois Lane and he accidentally breaks Jimmy Olsen's back when attempting to give him a hug. Meanwhile, Green Lantern is dreaming about losing his identity to the ring to the point where he becomes transparent, and the Flash dreams of being unable to turn off his Super Speed and being trapped in a world where everything else is standing still.
In Justice League: Doom the plan against Green Lantern relies on this trope.
Steven Universe:
- "Mindful Education" has Steven and Connie both dealing with this, Connie from attacking a kid who bumped her out of reflex and the All-Loving Hero Steven from being unable to save Jasper, poofing Bismuth and sending Eyeball out of his bubble when they were lost in space.
- The movie gives us Spinel's Heel Realization. She was literally made to be Pink Diamond's friend. She enjoyed being Steven's friend. And then she reactivated the injector that would kill all organic life on Earth when she thought he was going to use the rejuvenator on her.
- Spoilers for the Steven Universe: Future: This entire followup series is this for Steven. Turns out that saving the universe has left him without any life-changing goals to pursue and instead created a vacuum for all the pent-up trauma and anger at his mother's irresponsibility to surface. This isn't helped by all his friends and family members moving on with their lives, or sudden bouts of serious Power Incontinence (both of which he conceals from his family, despite their repeated attempts to offer help and support). This eventually culminates in Steven accidentally shattering one gem, then nearly shattering another. By the penultimate episode, his inability to live up to his (mistaken) belief that his friends expect him to be always and only an All-Loving Hero causes him to cross the Despair Event Horizon, triggering his corruption into a Pink Kaiju.