According to Sara C. Mednick, PhD, research scientist at the Salk Institute at La Jolla, CA, and author of the book Take a Nap, "our biological rhythm telling us when to sleep and wake changes across the lifespan. In older adults, those signals become weaker, and people develop changes in sleep pattern."

That said, there are some recommended methods for a nap that will leave you refreshed. "Typically, between one and three in the afternoon, you feel a bit of an energy dip," Dr. Mednick, says. "You can, within those hours, get on a schedule with your body. A nap of reasonable length is no longer than an hour and a half. That length of time gets you through a full sleep cycle. Also, you don't want to be sleeping too close to bedtime. Leave at least a three-hour window before beginning nocturnal sleep."

Being guided by moderation is the key to a nap that leaves you more energized than tired. "There's no benefit to napping beyond an hour and a half," Dr. Mednick stresses. "Beyond that, you're relaxing into the next sleep cycle."