Naps: How Long Helps and When They Hurt

A nap can be useful or it can work against you, and the difference is mostly length and timing. The same 20 minutes that sharpens an afternoon can, stretched to 90 minutes at 5 pm, push bedtime later.

Why length matters

Sleep moves through stages. In the first several minutes you are in light sleep, which is easy to wake from. After roughly 20 to 30 minutes, many people drop into deep sleep, the slow wave stage the body protects most.

Waking out of deep sleep is what makes the heavy, groggy feeling called sleep inertia so much worse. The brain is pulled out of its deepest stage before it is ready, and it can take 15 to 30 minutes to clear. That is why someone who naps for 45 minutes often feels worse for a while than before the nap.

A nap of 10 to 20 minutes stays mostly in light sleep. You wake easily, and alertness and reaction time improve within minutes. For most adults this is the length that helps.

A nap of about 90 minutes is the other workable option. It covers a full sleep cycle, so you tend to wake from lighter sleep at the end. It costs more time, and it costs the night more.

Why timing matters

The drive to sleep builds the longer you are awake. A chemical called adenosine accumulates in the brain through the day, and that pressure is a large part of what puts you to sleep at night. A nap spends some of it.

A short nap in the early afternoon spends very little. A long nap late in the day spends a lot, so bedtime arrives with less pressure behind it. People then lie awake, fall asleep later, and need another nap the next day. Ending a nap before about 3 pm keeps most of that drive for the night.

When napping is a signal

An occasional nap after a short night is normal. Needing a long nap most days is different. In adults, regular long daytime naps are often a sign that night sleep is not doing its job, through too few hours, broken sleep, or a sleep disorder such as sleep apnea.

A few questions are worth asking:

• Are you sleeping at least 7 hours a night?
• Do you snore, or wake unrefreshed even after a full night?
• Do you fall asleep without meaning to, while reading or as a passenger?

If the answer to the last two is yes, the nap is not the thing to fix. The night is.

For most people the rule is simple. Keep it to 10 to 20 minutes, finish before mid afternoon, and treat a daily need for long naps as something to look into.

If you are tired every afternoon despite a full night in bed, that's the kind of thing we look at.

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This article is educational and is not medical advice.