Once when I attended Global Game Jam, I worked on a game pretty much 36 hours straight, excluding some lunch breaks. Didn't sleep for 46 hours.

Gotta say, was a pretty weird feeling to wake up to tuesday when I went to sleep like 4 AM on monday. I slept over 20 hours. I remember waking up at one point and thinking that I'm still tired, so I'll just go back to sleep.

That was the one time when I truly 'slept a day away'.