The five stages repeat every 90 to 120 minutes. Stage one can last up to 10 minutes, stage two until the 20th minute. Extenuating circumstances, like manning the controls of a jet, aside, experts believe that the optimal power nap should roughly coincide with the first 20 minutes in order to give you full access to stage two's restorative benefits. In addition to generally improving alertness and stamina, stage two is marked by a certain electrical signals in the nervous system that seem to solidify the connection between neurons involved in muscle memory. "It's like a welding machine," says Mednick. "When you wake up, your neurons perform the same function as before, but now faster and with more accuracy," making the 20-minute nap indispensible to the hard-working athlete looking to straighten out his putter or baseline shot.

Mednick's most recent research also shows that power naps can lift productivity and mood, lower stress, and improve memory and learning. In fact, Mednick has found through MRIs of nappers that brain activity stays high throughout the day with a nap; without one, it declines as the day wears on. Tell that to the boss next time he finds you passed out at your desk.