Power napping

For a quick boost of alertness, experts say a 10-to-20-minute power nap is adequate for a quick recharge.

If you take it longer than 30 minutes, you end up in deep sleep. 

Have you ever taken a nap and felt worse when you woke up? That’s what’s happening.....You’re sleeping too long and you’re going into a stage of sleep that’s very difficult to get out of.

For cognitive memory processing, however, a 60-minute nap may do more good. 

Including slow-wave sleep helps with remembering facts, places and faces. 

The downside: some grogginess upon waking.

Finally, the 90-minute nap will likely involve a full cycle of sleep, which aids creativity and emotional and procedural memory, such as learning how to ride a bike. Waking up after REM sleep usually means a minimal amount of sleep inertia.

(Sleep inertia is a physiological state characterised by a decline in motor dexterity and a subjective feeling of grogginess immediately following an abrupt awakening.)

Summary - Napping even for 5-10 minutes creates a heightened sense of alertness and increased cognitive ability in comparison to no nap. 

So really, you want to be taking a 10-20 minute nap for a quick recharge, or a 60-90 minute nap for a deep sleep rejuvenation.

In addition to those recommendations, one surprising suggestion is to sit slightly upright during your nap, because it will help you avoid a deep sleep. And if you find yourself dreaming during your power naps, it may be a sign you’re sleep deprived.