I had a gig Friday night and was plucking particularly hard during one of the songs... I felt something im my forearm then my hand locked up. I could only move one finger. I finished the song and then played the last 2 songs of our performance. My hand locked up another 3 times. I would have to sit out a whole measure or two before it would work again. This happened to me once before. Does anyone know what this is? I didn't feel much pain but I literally lost control of my hand movement. It's really scary.