Naps are perfectly normal in most all of the world. You've heard of "siesta", right? And there are physiological reasons for it. Many studies have shown that it is perfectly normal to experience a short period of tiredness in the afternoon, even when fully rested. Hence, siesta in many countries.
Many studies have also shown that power naps are very effective in improving cognitive abilities related to many tasks, especially if sleep-deprived, but still helpful even if you had a full-night's sleep.
And even without the studies, I know it helps me. I'm a definite power napper, as are several of my coworkers.