When I speak to students about the importance of getting enough and good quality sleep, they almost always ask about naps: are they good? I think they want my permission to take naps because they are unsure or guilty about taking naps.
A nap, almost by definition, is short, and it's not (in American culture) a daily event.
When I ask students how long their naps are, the answer is almost always at least two hours.
That's not a nap; that's a evidence of sleep deprivation. The body is calling out for more rest than what it's being given at night.
And your body, brain, and spirit need enough and good quality sleep on a regular basis. Your ability to think better and in a more sustained fashion will be improved. Sleep will help you be and stay healthy. And sleep helps you maintain a positive mood. Students who get or start getting better sleep tell me that they feel better about themselves.
Back to naps, if you are getting enough and good quality sleep, a short nap (20-30 minutes) can (according to the Weill Cornell Medical Center) also improve alertness and learning, as well as not interfere with your evening sleep. "Researchers at the University of California, Berkeley, find that a[longer nap] clears the brain's short-term memory storage center and makes room for new information. Snoozing for 20 minutes improves alertness and performance without leaving you feeling groggy." (AARP Bulletin, Jan-Feb 2013, pgs 12, 14.)