I play quite a bit of chess online. I've noticed the following:

When I'm depressed, I lose a lot of games and tend to give up without trying. Sometimes I quit the game altogether and watch my rating tumble down by a hundred points.

When I'm manic, I tend to lose a lot of games because I make rash decisions and don't think things through properly.

When I'm stable, I tend to win far more games than I lose. For example, I've won 14 out of the last 17 games I've played, and I've been feeling pretty well, with the exception of a little anxiety here and there.

I guess following my trends in chess would be one way to track my mood.

WB