Have you read the Welcome to Silent Hill series?? It's the story that keeps getting recc'd to me when I want to read something dark. I'm not sure it 100% fills your prompt but I thought I'd point it out just in case. (http://archiveofourown.org/series/19902)
Re: John&Sherlock. "Jacob's Ladder"/"Silent Hill"-inspired AU. Dark. Possible Drug Abuse/Overdose..