I have always wondered this. I know the optimal situation is to sleep for 7-9 hours straight through the night. But what I frequently do is sleep for about 4 hours, then wake up and have a very hard time falling back asleep. So usually I just lie there in bed awake. I know lying without sleep is not as effective as sleep, but I think it is somewhat effective at restoring the body. But usually I feel pretty well rested in the morning, even though I maybe only "slept" for 4 hours, but rested in bed maybe for another 4 hours. Is there any ballpark figure of the equivalent amount of "rest" it would take to equal 1 hour of sleep??