Hi Lex,
I think your instincts about anti depressants are right on the money.
I had the same reaction when I first went on pain meds, and after I started taking prozac everyday, I got better and was back to my cheerful self again.
Its weird, because flashes of anger and frusteration dont seem like depression per se, but they must be from that (the meds themselves are depressants, so if you already have it, the meds make it much worse)
Give it a try for a few weeks, if it doesnt help, you havent hurt anything by trying, and there are next to no side effects with the newer type anti depressants.
Good luck and let us know what you decide.
~Fabby