I've done this a lot, too. I think it is just something that depression can sometimes bring on. I feel guilty when I get depressed, too. I feel like I have a good life and should be happier, but sometimes it isn't that easy. And I tend to punish myself a lot whenever I start getting happy. I think something in my mind tells me I don't deserve to be happy, so I sabotage my happiness. Messed up, huh? The best way I get over it is to remind myself I do deserve to be happy, and it isn't always the worst thing if the depression gets the best of me. I'm constantly trying to stop being so hard on myself.