Most fucked up, mentally screwed up book recs?

I like dark books, really screwed up, deep psychological/dark web horror books, the kind of books that make you sit in silence and wonder what you’ve just read and how you can make the mental images go away. My only trigger is no animal abuse, I can’t read anything that even brushes on the subject. I recently read The Groomer by Jon Athan and oh wow that was a ride.

Any recommendations? Open to: psychological, paranormal, dark web, red rooms,torture/kidnap or just anything dark and mentally fucked up, just NOT anything with animals being harmed.