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What are the Four Stages of Sleep? [2021]

We all know that we need approximately seven to eight hours of sleep per night. In fact, getting that amount of sleep has positive effects on your metabolism, keeps your immune system functioning, and keeps your memory sharp.

But what does sleep actually mean? Is there a sleep definition?

The Merriam-Webster dictionary defines sleep as “the natural periodic suspension of consciousness during which the powers of the body are restored”.

But that doesn’t cover the whole meaning. Your body goes through four key stages during your sleep cycle. You must achieve each while sleeping to feel as refreshed as possible when you wake up.

Table of Contents

The Four Stages
Stage 1
Stage 2
Stage 3
Stage 4
The Final Word

The Four Stages

The four stages of sleep split between periods of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.

Three of these sleep phases fall into the NREM category.

NREM Stage 1

The first stage of sleep typically lasts for between 5 and 10 minutes. This is the period during which you’ve closed your eyes and may start drifting in and out of consciousness.

rem cycle

Many people call this dozing. You’re on your way to going to sleep, but you’re not quite there yet. It’s easy to wake you up during this period, plus you won’t feel too disoriented immediately after coming out of the first stage of sleep.

NREM Stage 2

At this point, your body has reached a light sleep. It’s in the preparation stages for the deeper sleep that will replenish your body.

During this stage, your body temperature will fall slightly, as will your heart rate. Your body starts entering a relaxation mode. However, it’s still fairly easy to wake you up from this stage of sleep.

stages of sleep

NREM Stage 3

The final stage of NREM sleep is also the deepest. During stage 3, your body actively repairs your muscle tissues, boosts your immune system, and strengthens your bones.

You’re also much more difficult to wake up during this stage, as anybody who’s ever slept through an alarm can tell you. Should you wake up before you exit NREM stage 3, you’ll feel disorientated for several minutes afterward.

Interestingly, the length of stage 3 shortens as you get older.

Although you need just as much sleep as you did in your younger days, you’ll sleep more lightly than you did before.

The REM Stage

The fourth stage of sleep is the one that most people commonly associate with dreaming. Typically, your body enters the first REM stage after about 90 minutes of sleep. It then exits and enters REM stages multiple times during the night, until you wake up.

Why is rem sleep important?

Rem cycle is the most restorative time during the sleep.

The first of these REM periods lasts for about 10 minutes, with subsequent REM periods lasting longer each time. If you sleep for eight hours, your final REM period could last for about an hour. You usually re-enter NREM stage 3 after coming out of a REM stage.

rem cycle

During REM sleep, your eyelids flicker rapidly and you’ll often experience vivid dreams. Your heart rate increases again and you’ll take shorter breaths than when you’re in NREM stage 3.

Much like with NREM stage 3, the amount of time you spend in the REM stage decreases with age. Babies spend about 50% of their sleep time in the REM stage, which drops to about 20% when you’re an adult.

The Final Word

As you can see, the sleep definition extends far beyond the basic definition you’ll find in your dictionary. To truly understand sleep, you must understand each stage, how they fit in your sleep timeline, and why it’s important to your sleep cycle.

Achieving a deep sleep each night helps your body to repair itself. Exercise regularly and create a healthy bedroom routine to ensure you sleep as well as possible.