I was playing Animal Crossing City Folk and one of my friends that I hadn't spoken to in a good while was visiting my town. I must have fallen asleep around 2 or 3 in the morning. I remember waking up around 5 or so with the controller on my bed and the game was still on.
I've fallen asleep during hundreds of games, but that's mostly because I game during long insomnia bouts until I pass out. If you're passing out during a game from boredom, I have a hint: play something else. Somehow I'd assumed that was common sense until now.