I just got back from the weekly At Least We're Hot jam session. I thought that I played pretty well tonight (I play fiddle with this particular group). At first I thought it was because it had only been five days since our last jam, rather than a whole week, so I was a bit more in practice. But then, on my drive home, I was reflecting that I probably played about as well (or as badly) as usual, and for some reason I percieved it as better. Maybe it was because I was in a good mood. Maybe it was because of my new shoes:
In any case, I think that often happens---that our perception of how we play has little to do with how we actually play. Sometimes people will get very discouraged over having a bad playing day, but it almost always is not as bad as they think. (Of course, it works in the opposite direction, too. If you think you played awsomely, it may not have been much better than average.) It's the same principle by which I judge my hair. Some days I think it looks great, for no particular reason; some days it looks awful, for no particular reason. But to everyone but myself, it probably looks almost identical.
I don't know what factors go into how we percieve our playing, but take that into account when you think you've played badly. Don't get discouraged. But then, when you think you're playing awesomely, try and hold onto that feeling for as long as possible. It can only be good for your playing!