Sometimes with depression, something can change (maybe you just had a good night's sleep or something like that) and it can lead to another positive thing and then to another and then suddenly you find yourself in a much better place.

Of course, it can go the other direction too, which is terribly frustrating.

I tend to ask myself "what's different", too, when I have a sudden mood change, but I'm not always able to figure out what changed.

I'd say just grab it and go with it. I'm glad you're feeling somewhat better.