A nap of 60 minutes improves alertness for up to 10 hours. Research on pilots shows that a 26-minute "Nasa" nap in flight (while the plane is manned by a copilot) enhanced performance by 34% and overall alertness by 54%. One Harvard study published last year showed that a 45-minute nap improves learning and memory. Napping reduces stress and lowers the risk of heart attack and stroke, diabetes, and excessive weight gain.
Limit your nap to 45 minutes or less, if you need to spring into action after dozing. Otherwise, you may drift into slow-wave sleep. Waking from this stage results in sleep inertia, that grogginess and disorientation that can last for half an hour or more.
But you might want to take a long nap, at least 90 minutes. Many of us get about an hour to an hour-and-a-half less sleep a night than we need. One recent study shows that the sleep-deprived brain toggles between normal activity and complete lapses, or failures, a dangerous state of slowed responses and foggy inattention. Sound familiar?
Naps of 90 to 120 minutes usually comprise all stages, including REM and deep slow-wave sleep, which helps to clear your mind, improve memory recall, and recoup lost sleep. Longer naps in the morning yield more REM sleep, while those in the afternoon offer more slow-wave sleep. A nap that is long enough to include a full sleep cycle, at least 90 minutes, will limit sleep inertia by allowing you to wake from REM sleep.
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