Oh... I feel so sorry for you. That happened to me once before, where, I was just doing some homework, and I suddenly became depressed. I didn't feel like doing anything I liked, and I couldn't even play with my tamagotchis!
Does it have something to do with school? Cause' that's what happened to me. It was the whole, "Getting up and doing the same thing at the same times every single day...", you know, school. Just tell me all about it, I'm happy to help you out.