Wolfwood, my roommate did that once and he was sober.

I've gotten so high that I space out and the joint falls off my mouth and on my lap, and I react after I burn myself. I freak out, slap it off me, than I'm like "Oh shit!" pick it up and the same thing happens...then I just REALLY concentrated so I could finish the joint.

I've also burned my fingers, sometimes the flame just ends up flowing right to my hand. I think I once burned some strands of my hair (it's pretty damned long) lighting up my pipe.