Mine's inherited and atypical, but the sorts of things being suggested here have helped, e.g. a SSRI. I strongly recommend getting a copy of this book: http://www.amazon.com/Feeling-Good-New-Mood-Therapy/dp/03808... or any other good guide to cognitive therapy, which has an added behavioral aspect nowadays. Therapists ought to be versed in CBT, and if things are bad enough they're worth a try.