Today's three-minute lesson

Sleep Happens in Cycles

Sleep is not one continuous state.

Throughout the night, your brain moves through a series of sleep cycles. Each cycle contains different stages of sleep, ranging from lighter sleep to deep sleep and rapid eye movement—or REM—sleep.

Each stage plays a different role.

Deep sleep is particularly important for physical restoration, while REM sleep is associated with dreaming, memory and emotional processing. Lighter stages help your body move between them and make up a significant proportion of a normal night's sleep.

The structure of these cycles changes as the night progresses.

You tend to experience more deep sleep during the earlier part of the night. Longer periods of REM sleep usually occur towards morning. This means the final hours of sleep are not simply more of the same—they contain a greater proportion of a stage your brain still needs.

You may have heard that every sleep cycle lasts exactly 90 minutes.

It is a useful approximation, but not a rule.

The length of a sleep cycle varies between people and can change throughout the same night. Trying to calculate the perfect bedtime by counting backwards in 90-minute blocks can create a false sense of precision.

Your body does not sleep according to a stopwatch.

It is also completely normal to wake briefly between cycles. Most of these awakenings are so short that you will not remember them the following morning.

Occasionally, you may become more fully aware of one.

This does not necessarily mean that something has gone wrong or that the rest of your night will be disrupted. You may simply have reached a lighter stage of sleep before beginning another cycle.

The way you respond can make a difference.

Checking the time, reaching for your phone or beginning to calculate how many hours remain can turn a brief awakening into a period of alertness. The time itself rarely helps you return to sleep, but it can give your mind something new to worry about.

If you wake during the night, try not to treat it as a problem that must be solved immediately.

Keep the room dark, avoid checking the clock and give your body an opportunity to move naturally into its next period of sleep.

Your task tonight is simple: remove the clock from view before you go to bed. Once your 30-minute bedtime alarm has sounded, put your phone aside for the night so it is not the first thing you reach for if you wake.

If you do wake, remind yourself that brief awakenings are a normal part of moving through the night.

You do not need to manage every sleep cycle.

You only need to give them enough time and space to unfold.