My first GD: A natural disaster!!

This is bout my first GD, which happened like, a week ago. It wasn't a real GD, just a mock one, to give us freshers a taste of what GDs really are about. But that isn't the important thing here; the imp thing is that I didn't speak a word through the entire thing, except for when the judges asked me to conclude and thus forced me to open my mouth! I've been back to that moment so many times eversince, but I just can't understand what happened to me then. I have spoken before, in the very same college, and that too, all alone!! and to a bigger crowd! I knew the stuff to say and knew it'd be better than what anyone else had been sayin. It was as if I had just lost my voice!! I actually find that scene funny when I think bout it: I talk absolute nonsense, non-stop, and drive everyone nuts; but when I was asked to talk, I completely shut up!!