It's Kind of a Funny Story, by Ned Vizzini
I've read Ned Vizzini's two previous books, Teen Angst? Naaah... and Be More Chill, and they were both hilarious. It's Kind of a Funny Story is also funny (heh), occasionally to the point where I was laughing out loud. It also hits on a different level though, and Craig's recovery is one of the most life-affirming things I've ever read.
If nothing else, read the book for the ending. While it's still directed towards Craig, it's also kind of a message for everyone who's ever fought battled against suicidal feelings.