If you are feeling so tired that you think a nap is in order, here's a way to make sure that your nap results in your being refreshed, not groggy.

The first key is to limit the length of your nap. You don't want to sleep more than 30 minutes. If you sleep more than 30 minutes, you enter a much deeper phase of sleep and it will take you a long time to wake up after your nap. The result of this is that you'll feel just as tired as you did before you took the nap. Only nap for 30 minutes.

The second key is to drink some coffee, tea, soda, or some other beverage that has caffeine in it right before you take your nap. Yeah, I know it sounds weird to do that since you want to sleep, but caffeine takes 30 - 40 minutes to take effect. If you drink it right before you take a nap, then it'll be kicking in right when you are getting up from your nap.

The combination of the refreshing short nap, and the onset of the caffeine will result in your feeling refreshed and energized when yo get up from your nap.