The more busy or stressed you are, the more rest you need. In busy times, a nap can save your day so learn to listen to your body and its needs. You don't even need to fall asleep to feel re-energized. If you have the time, grab a blanket, put on some relaxing music and shut your eyes. If you haven't got the time for a lie down, just simply close your eyes whenever you have a chance - on the toilet, at your desk, when waiting for a red light etc. Even a few seconds makes a difference.
Afterwards you'll feel relaxed, more positive and more energized. A nap a day keeps the doctor away?!