wow that's so odd the same thing happened to me yesterday. I suddenly felt like I had no future and my life was over, even though I was happy only hours earlier. And nothing really happened to make me feel so miserable. I ended up crying myself to a restless sleep, then woke up in the morning and was irritable and pretty much mad at everyone. I help with a kids' ministry program and I went to church with the kids I help with and they made me feel better. Do I feel really happy? No. But I don't feel as miserable.
I guess all I'm saying is get out and try to do something and give it some time.
Hope this helps!!