I guess it would probably depend on how tired you were. But lets say you only got 4 hours of sleep the night before. Would you go out and ride the next day?
I can't ride if I'm tired. Its to much of a risk so for my own safety I don't. I almost found out the hard way. Decided to go for a ride after only getting 3 hours of actual sleep the night before. Almost got plastered by a semi.
I need a minimum of 7 hours of quality sleep to be able to function on a bike, or in doing anything for that matter not just riding.
Last night I would have gotten 7 hours, except I kept getting up, had stomach problems. I'll spare you the details but you get the idea. So because my sleep was interrupted I won't ride tonight, for my own safety. I know it sounds like a piss poor excuse, but hey I'd rather skip one day of riding then ride, get nailed by a vehicle and have to spend several days or weeks off the bike.
How about the rest of you? How much sleep do you need to be able to function? I'm talking about quality R.E.M. sleep here ok.