Jason,
I like the line in your signature line, "We were meant to live for so much more..." I think that sometimes when things have been good for me, I do get tired because I don't think that I deserve them. Kinda my way of seeing to it that I didn't enjoy myself too much. I mean, after all, anyone who went back for the abuse, must be some kind of creature who doesn't deserve anything good in his life.
This may not be in any way connected to what you're dealing with, it could be completely chemical, as you were thinking. Just a thought.
Hopefully, one of the guys who are pharmaceutically blessed will come by with something more specific to say.
David