Naps longer than half an hour are more likely to end during deeper sleep.

The longer version

Given enough time, a sleeper sinks into slow-wave sleep, and being roused from there brings grogginess, confusion and slowed thinking that can last several minutes or longer. Simple tasks suffer most in the first minutes, and complex decisions take longer to come right. Researchers refer to that after-effect as sleep inertia.

Longer naps also buy more of the later dream-filled phase, which is why an hour or more can produce vivid imagery. The trade-off between recovery and grogginess is one reason brief dozes are favoured during a working day. Accounts of midday rest in warm climates, ancient and modern, describe similarly short sleeps taken in the heat.

Where this entry sits

This collection gathers curious details about sleeping and dreaming, from nightly brain stages and body clocks to naps, yawns and unusual animal habits. It also covers how bedtime customs have changed across centuries, without offering any advice. The full list sits on the Sleep and Dreams page, where every entry is listed in order.