There's a book that's not necessarily about self harm but more about suicide and this boy's experience in the mental hospital after a failed attempt to commit suicide. I thought it was a really good book and I think you should look into it even though it's not exactly what you're asking for. It's called Suicide Notes by Michael Thomas Ford. Amazon Link - http://www.amazon.com/Suicide-Notes-Michael-Thomas-Ford/dp/0060737573
This one. It's absolutely Suicide Notes.