What is the optimal length of time for a nap?
Naps can be short (15 to 30 minutes) or longer; both short and long naps can increase alertness and be useful.
- Take into account that sleep becomes deeper the longer you sleep, reaching the deepest level (slow-wave sleep) in about 1 hour. If you awaken after about 1 hour of sleep (when in deep sleep), your functioning might deteriorate considerably due to "sleep inertia." 15,17
- If you wake up from a nap in either 20 minutes (before going into deeper sleep) or about 90 minutes (predicted to be the end of a sleep cycle), grogginess from sleep inertia may be less on awakening and may go away more quickly (within 15 to 30 minutes), since you will likely awaken from light stages of sleep.
- However, if you are very sleep deprived when you start your nap, your brain may progress to deep sleep more quickly. As a result, sleep inertia may last longer making it more difficult for you to wake up and feel alert even after a short time asleep.
- If you work a daytime schedule, a brief (<20-minute) nap is recommended. Set an alarm for 15 to 30 minutes to wake up. A brief nap can increase alertness for a couple of hours after the nap, with less grogginess,1-7,9-13 and does not disrupt subsequent sleep at night because it does not reduce the homeostatic buildup of pressure for sleep.24 If you wonder whether you actually fell asleep during a brief nap period, some signs indicating light sleep are fragmented visual images, a sudden muscle contraction, or a sensation of starting to fall.