Mind games?

I know I'm not the first person to find that the expectation of a lousy performance often brings about the opposite result.  I remember the first time that happened to me - I was in Riga, Latvia and had to perform Sarasate's Introduction and Tarantella with the flu.  I knew nothing good could come of the performance - I was exhausted and could barely even hear because of congestion.  But I remember playing on stage and being amazed at how well everything was going.  I was hitting notes that were usually "iffy" and didn't even feel the slightest bit nervous.

Our minds play ridiculous games with us as performers, I'm learning this more and more every day.  Tonight I had a performance of the Beethoven Violin Concerto in my studio's recital in Duncan Hall.  For the past few days my left hand has been feeling.. strange. "Twitchy", you might say.  Today it was horrible, I couldn't do anything without my hand shaking and my thumb involuntarily twitching every so often.  I thought, "there's no way I'm going to be able to get through this 40 minute concerto tonight."  But I knew I needed to do it, so I practiced a little in the afternoon, being careful not to overplay, and pulled myself together for the performance.

Even though I was worried about my hand, I wasn't nervous.  There was a sort of paradox going on with my thoughts.  I would think that worrying about my hand not feeling normal during a performance would make me more nervous.  Instead my focus shifted from "I have to give a perfect performance!" to, "my hand isn't feeling right, I can't expect a lot, so I'll just go out and do the best that I can."

The performance went wonderfully! It wasn't perfect, it never is, but I had no major problems and was really happy with how it all went.  During the first movement, I felt slightly like I was having to control the shaking of my hand.  It's really strange when a part of you is shaking and it's not from nervousness.  As the piece went on though, I felt more control over it and more at ease.  I still felt really shaky for about 20 minutes after I was finished, but now I'm typing and my hand feels almost normal.  It's certainly much better than it was over the past few days.

So what does that mean - it's all in my head?  I'm not sure.  Part of me hopes so (though that would be annoying), but most of me thinks it's some sort of small issue that's exacerbated by adrenaline preparing me for a performance.  My hand hasn't done that before though, so I need to go get it checked out in case there's a problem.  I can say for sure, I'm definitely taking a break from violin in the morning.

Who else has a story about strange physical phenomena before or during a performance?