On a stage, after the show, when we were loading out System of a Down. I had been going from gig to gig back-to-back-to-back, and had not slept in about 65 hours. My body decided to shut down while I was waiting for some truss to land. I fell asleep for a moment, and woke up from the sensation of freefall as I was about to hit the deck. That sucked.
There was one time when I fell asleep on a road case an arm's reach from the subs at the Warped Tour. I was out for about 15 minutes, and the whole time in my dream there was really loud and annoying shitty music playing. I woke up really cranky and with a headache.
I've got loads of anecdotes related to falling asleep on, or near, stages.