Yeah, I get this too. It's like, if I start to feel happy or carefree or enjoying things, it's like I remind myself "hey, you're supposed to be miserable" like that's my baseline or it's what I deserve or something. It's awful. Like I said earlier, I'm not suicidal or anything, and most of the time I am together enough that I feel fine - but I can't remember the last time I felt truly, really happy and relaxed for more than a very brief period of time. And I'm sick of it... hence going to talk to someone. I really hope it helps.
Thanks again to everyone for chiming in.