When I was in HS (15 or 16) my school had an all night "walk-a-thon" and they had a helium tank for the balloons. We were huffing on it to talk with a helium voice. I pulled a couple of deep breaths when we saw some people and started running over to them. Mid-stride I fainted and landed face first on a gravel track. The cop who just saw me take a face-plant comes over to me, lying awkardly in the middle of the track with my face thrashed and asks if I'm okay. As I was coming to, I was semi-conscious, had no recollection of what had happened, thought I was in the grass, opened my eyes and said "yeah, I'm just lying down." God knows what he must have thought.