Here's what NASA says is the perfect length for a power nap

Mass Communications Specialist 1st Class Peter Blair/US Navy

A Navy chief sleeps between exercises during a combined field training exercise near Azusa, California.

• Everyone gets groggy when mid-afternoon rolls around, and a nap is usually the best way to recharge.
• Now NASA has found the ideal length for some midday shut-eye.

Everyone gets that "2:30 feeling." Military personnel happen to get it at all times of day. Maybe you're on mids. Maybe you're in transit from Afghanistan to Japan. Or maybe you're being punished for doing something stupid. It happens. But we don't always have access to Five Hour Energy shots, and sometimes coffee isn't cutting it.

The best thing to do is give in: have your battle cover you while you rack out for a few minutes.

Or maybe fifteen? A half-hour? A full hour? How long is the proper power nap? Thanks to NASA, we have the answer.

US Marine Corps.

There's no shame in needing a little afternoon siesta. Anyone who swears by the power nap will tell you that nodding off for a few minutes can revive them for hours. Just don't let the First Sergeant catch you.

But if you can get away with it on duty, you (and your coworkers) will be grateful to find you more productive and operating at a higher level. It's a natural part of human circadian rhythm, you're going to be intensely sleepy twice per day. You can't stop it, none of us can.

NASA's research showed that naps really can fully restore cognitive function at the same rate as a full night's sleep. The space agency found that pilots who slept in the cockpit for 26 minutes showed alertness improvements of up to 54% and job-performance improvements by 34%, compared to pilots who didn't nap. But 26 minutes might be a little long.

Lt. Col. John Hall/173rd Airborne Brigade

Paratroopers catch some sleep after working through the night to prepare for an early morning combat jump in Italy.

"Napping leads to improvements in mood, alertness and performance [such as] reaction time, attention, and memory," according to Kimberly Cote, Ph.D, Professor of psychology and neuroscience at Brock University, who co-authored a similar study with researcher Catherine Milner. "Longer naps will allow you to enter deeper sleep, which will contribute to the grogginess - also called sleep inertia - experienced upon awakening and disrupt nighttime sleep."

Cote and NASA suggest taking power naps between 10 and 20 minutes long. You'll get the most benefit from a sleep cycle without any of the grogginess associated with longer sleeping periods. You don't need to get through all five sleep stages, just the first two. Even just getting to stage 2 sleep for a few minutes will revive a napper enough to give him or her a new outlook on the day.

So get cozy and rack out for a few. It's actually better for everyone.