For many of us, taking an afternoon nap is a great way to refresh when we’re feeling sleepy. The September 2008 issue of Harvard Men’s Health Watch discusses napping, its risks, its benefits, and tips to make it work for you.

People who are sleep deprived feel groggy during the day and may fall asleep when they least want to, perhaps at their desks or, worse, behind the steering wheel. Poor sleep at night may be caused by simply not devoting enough time to sleep or by medical problems that disrupt sleep, such as restless legs syndrome and obstructive sleep apnea. And in some cases, daytime sleepiness can result directly from medical problems such as depression or an underactive thyroid.

Voluntary napping, on the other hand, is not a sign of sleep deprivation, illness, or aging. In fact, a “power nap” can be helpful as well as enjoyable. Many studies of shift workers and other volunteers have reported that a nap as brief as 20 minutes can improve alertness, psychomotor performance, and mood.

Naps, however, aren’t trouble-free. One problem is sleep inertia, or grogginess and disorientation that may accompany awakening from deep sleep. The second problem is nighttime wakefulness.

To get the benefit of a quick snooze without being caught napping, Harvard Men’s Health Watch suggests the following tips:

• Plan to take your nap at a good time in your daily sleep-wake cycle; for many people, sometime between noon and 4 p.m. is best.

• Don’t sleep too long; a 20- to 40-minute nap may refresh your day without keeping you up at night.

• Give yourself 10 to 15 minutes to wake up fully before you resume a demanding task