I think naps are good for you, and I nap every day. Napping may even make you smarter. One study compared a people’s ability to learn after no sleep, a 30-minute nap, or a 60- minute nap. Those who had a 30-minute nap did better than those who didn’t nap, while those who took a 60-minute nap did far better than those who took only a 30-minute nap.
When you start a nap, your eyes are kept still, called non-rapid-eye-movement sleep. You drop down from stage one sleep into a deeper stage two, then a deeper stage three, and then your eyes start to move rapidly back and forth. This is called Rapid Eye Movement sleep, or REM sleep. This study shows that you learn better if you wake up right after non-REM sleep (stage two), and you get more non-REM sleep in a 60-minute nap than a 30-minute nap.
If you feel tired most afternoons, you are normal. In many parts of the world it is traditional to take an afternoon nap or siesta. Studies of office workers and school children show that people work best in the early morning. As the morning progresses, they lose their ability to concentrate. Then they go out to lunch and function way below their capacity for the rest of the day. It gets worse as you age. Tiredness is a signal that your brain needs a rest. Find a quiet place to lie down and take a nap.
Also read my report on sleep apnea, a more serious cause of daytime sleepiness.