Did you know that feeling sleepy in the afternoon is part of the normal human circadian rhythm? Humans typically have two periods in which they feel intensely sleepy. One is usually in the very early hours (around 3 in the morning), and the other is in the early afternoon, about ten hours after the first. You know that taking a nap can help increase your productivity and your mood, but do you know that there is a proper way to take a nap?
If you want to increase your concentration, take a short nap of about twenty minutes.