I have had too many great ones to list, so I'll tell about a bad one.
Summer of 91' at Soldier Field, seeing the Dead for about my 10th time. My buddy, who had always been a little shaky while tripping anyway, got freaked out by the tapers that we were sitting near. We were being a little loud, and all they asked was for us to keep it down a bit, but it ran away in his head, and before I knew it, he was gone.
I heard he passed a friend near the concession stand, and asked him if "he was with them?", yeah of course my friend said, and then he was really off.
The next we heard from him, it was the next day, we awoke at the Congress Hotel, to a call from a friend in StLouis. "What did you do to Matt?"
Apparently he left the venue, and made his way to a hotel, where he stuffed a mexican valet in a trash can and stole a car. Proceeded to hit the highway before he stopped somewhere about 2.5 hours outside of Chicago. He called a friend and told him to come get him.........
Talk about a long strange trip......