Same thing happened to me in March 04. Turned a mic on, couldn't let go, couldn't speak to get my mate to turn the PA off. He didn't see what was happening fo a good few seconds cos he was playing with the EQ on the PA.
Like JD1 said earlier, the noise you can hear or feel or whatever going through your body is horrible! I had the mic in my right hand and had hold of the neck of the guitarist's guitar in my left. The strings burned through my index finger and I've got 3 nice guitar string scars on it now, a few other little scars all over both my hands and had to have 2 areas skin grafted on my right hand. One burn at the bottom of my little finger was right to the bone.