Suggest disturbing books. Books that made you gasp, made your skin crawl, made your stomach drop.

Can be fiction, nonfiction, fantasy, true crime, etc. I'm not picky on genre. Hit me with something that will give me visceral reactions to the text I'm reading. Disturbing, or psychologically troubling, I want to read the books that have stayed on your mind long after you finished them because of their eerie/disturbed contents. Books that made your skin crawl and stomach drop. Your "What the eff" books. Thanks!