The 4 Sleep Stages Explained

Generally speaking, there are 4 sleep stages sub-divided into light and deep sleep. The first two stages [light sleep] initiates the sleep process as your body begins to relax and your heart rate/breathing slow down. This paves the way for the last two stages [deep sleep] which promotes muscle growth and repair, not to mention, waste removal from your brain. 

When you hit the bed after a long day, you have no idea what’s going on behind the scenes in Zzz world. To you, you’re simply sleeping...and if you had a good night’s sleep, it often looks like you closed your eyes one minute and the next minute you’re awake and ready to hit the road.

So, what happens exactly in-between sleep and wake time?

A lot! As you hit the bed and doze off, your brain and body don’t. Actually, sleep time is time for the body to restore dead cells and for the brain to refresh and recharge for the next day’s activities. 

While sleep is sleep as far as you’re concerned, sleep experts have found there are 4 stages to sleep. And how you move from one phase to another goes a long way in determining how well-rested and recharged you’re the next day.

In an ideal situation, you go through several 90-minute sleep cycles that sample each phase of sleep. And each stage has certain restorative benefits that play a super important role in supercharging your mental and physical health. 

However, the time spent during sleep in each stage or phase varies night by night and individual by individual. 

The stages of sleep and what goes on behind the scenes

Before now, sleep was categorized into two: Non-rapid eye movement [NREM] and rapid eye movement [REM]. During NREM sleep, your eyes remain still [without movement] while REM sleep involves your eyes moving rapidly under your eyelids.

So, below are the 4 sleep stages and their distinct characteristics…

Stage 1

Within minutes or even seconds of dozing off, your brain produces something called alpha and beta waves and your eye movements gradually slow down. This first phase is short-lived, lasting only for about 7 minutes or so. In this light sleep stage, you’re kinda alert and can be easily awoken by little distractions.

Stage 2

During this stage, your sleep is still fairly light, and your brain produces sudden increases in brain wave frequency called sleep spindles. It’s during this sleep stage that your muscles relax, respiration slows, heart rate decreases, body temperature drops -- and sleep really sets in. If you were only looking to power-nap…then this is the time to wake up.

Stage 3 & 4

So, this stage ushers you into the deep sleep phase where the brain starts producing slower delta waves. In this stage, you won't experience any eye movement or muscle activity but it becomes a little harder for you to be awakened as your body becomes less responsive to external stimuli. 

More delta waves are produced here, moving you into an even deeper, more restorative stage of sleep. It’s at this stage that the body repairs muscles and tissues; stimulates growth and development; boosts immune function, and helps you refresh and recharge for the next day.

How about REM sleep?

Well, REM [rapid eye movement] sleep is associated with dreaming, memory, learning, critical thinking, and problem-solving. REM sleep is vital in recharging your mind, but as you age, the frequency and time spent in this sleep stage decreases.

During REM sleep, respiration increases, blood flow also increases to genitals, and brain activity is super high, leading to vivid dreams sometimes.

So, that’s it folks -- but before you go…

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