Could be a carple tunnle kinda thing... Happens to me very rarely, when I've been on the computer a lot on the day of a gig, and only then during LONG killer fast songs...

I drop out to 'shots' for a few bars, and inbetween give my arm a quick stretch or a bit of a shake in a different direction than I've been playing in...

Time it just right, and the audience thinks yer doing it on purpose! LOL!!!!!