A nap is one of the few things that's free, works almost immediately and comes with no side effects. That is, as long as you get the length and timing right. Get it wrong and you wake up groggier than before.
Why naps sometimes backfire: sleep inertia
Sleep has light stages and deep stages. Wake up during light sleep and you feel fine quite quickly. Wake up from deep sleep and you get sleep inertia: that heavy, foggy, "where am I" feeling that can last from a few minutes to half an hour. The longer the nap, the more likely you are to be in deep sleep when the alarm goes off.
How long?
10–20 minutes: the classic power nap
In a well-known study, sleep researchers in Australia compared naps of 5, 10, 20 and 30 minutes in people who'd slept too little the night before. The 10-minute nap came out best overall. It improved alertness and performance almost immediately, and the effect lasted around two and a half hours. The 20- and 30-minute naps also helped, but people were groggy at first. The 5-minute nap did very little.
About 90 minutes: a full cycle
A nap of around 90 minutes usually takes you through a full sleep cycle, so you wake from lighter sleep. It's useful before a night shift or after a very short night. It's too long for a normal afternoon, since it can make it harder to sleep at night.
Avoid 30–60 minutes
That's the zone where you're most likely to wake up mid-deep-sleep and feel worse than before.
When?
- For most people the best time is early afternoon, when there's a natural dip in alertness.
- Avoid napping within a few hours of your main sleep, or you'll have less "sleep pressure" when you go to bed.
- If you have trouble sleeping at night, it's often better to skip naps altogether for a while.
Naps for night workers
Naps are one of the most useful tools for people who work nights. NASA studied this with long-haul airline pilots. Pilots given a planned 40-minute rest period in their seat slept for about 26 minutes on average, and were measurably more alert and performed better afterwards than pilots who didn't rest.
- A longer nap in the afternoon before your first night shift makes that night much easier.
- A short nap during your break, where your workplace allows it, gives a boost for the second half of the shift.
- Give yourself 10–15 minutes after waking before doing anything safety-critical, so sleep inertia can wear off.
- Never rely on a nap to fix drowsy driving once it's already happening: pull over first.
How to nap well
- Set an alarm, so you can relax instead of worrying about oversleeping.
- Darken and quiet the space: an eye mask and earplugs work wonders on a sofa or in a break room.
- Don't worry if you don't fall asleep. Lying quietly with your eyes closed is still restful.
- Try a "coffee nap": drink a coffee, then nap for 15–20 minutes right away. Caffeine takes about that long to kick in, so you wake up just as it starts working. It's best before a drive or a late shift, not in the evening. See our caffeine guide.
- Get light and movement straight after waking to shake off any grogginess.
If you need naps every day despite getting enough sleep at night, or you fall asleep without meaning to, talk to a doctor. Excessive daytime sleepiness can have treatable causes.
