It's mid afternoon, you just got back from lunch, and you're sitting at your computer. Suddenly, a little nap, just a few minutes, feels like a great idea. Should you indulge? To nap or not to nap in this Moment of Science.

Today, most sleep researchers say yes, go ahead and snooze. Afternoon naps tend to be made up largely of the most restful type of sleep, making them an effective way to catch up on the sleep you didn't get the night before. A short slumber in the afternoon can make you more alert and improve your mood, memory, and ability to make decisions.

It's not just coincidence that mid-afternoon is a prime time for naps. If you eat a starchy lunch, your body responds by making a sleep-inducing chemical called serotonin. And even more important, body temperature dips into a sleep zone in the late afternoon. It seems that we're naturally programmed to nap about twelve hours after we wake up from our nighttime rest.

Researchers agree that optimum napping time is between fifteen minutes and two hours. During a nap that's shorter than fifteen minutes, you never enter the most restful phase of sleep. But if you sleep for over two hours, you might not be able to fall asleep when you turn in for the night.

You'll probably need less sleep at night if you pick up the habit of drowsing off during the afternoon. Researchers have found that we sleep for about the same number of hours each day, no matter when we choose to slumber.