Tired young woman in white is sleeping. Sleep and Time concept. Clocks as backgroundWhen we’re sleeping, there’s a lot happening. It’s not just a time for us to rest and rejuvenate for the next day. In fact, once we fall asleep, our brain continues to be more active, our mind is circulating through a number of sleep cycles and crucial physiological processes are occuring. It’s worth understanding the stages of sleep to better recognize the deeper role it plays in our health and wellbeing. 

As we spend at least a third of our lives sleeping, we should pay as much attention to this facet of our humanity as we would in our career and relationships. And just like work, relationships and our families, sleep is complex and multi-dimensional. Continue reading to learn more about your different sleep stages and cycles.

Sleep is more dynamic than passive

Interestingly, before the 1950s, sleep research scientists believed that sleep was a time when our bodies go into a passive, “shutdown” mode. They thought the brain would turn off, the body would recover and we would restart again in the morning. However, they would eventually come to discover through brain activity recordings that this couldn’t be further from the truth. Through measuring eye movements and muscle activity, sleep studies revealed that a sleeping person’s brain is running through two main cycles: non-REM (rapid-eye movement) and REM sleep.

Understanding the Stages of Sleep 

Throughout one night of sleep, your brain will frequently cycle and repeat through these two equally important stages. 

What is happening during Non-REM sleep? 

You go through non-REM sleep before REM sleep. In the three stages of non-REM sleep, each stage can last anywhere from 5 to 15 minutes. Think of it as a slow build-up to a movie climax, or the rising action. The first two stages are fairly light, followed by a deep third stage.

Stage 1:

This is the time that you start to become drowsy and nod off. You’re essentially transitioning between being awake and falling asleep. Your heart and breathing begins to slow down, in addition to your eye movements. Your muscles relax. While this stage is brief (5 – 10 minutes), you can be easily woken.

Stage 2:

This stage lasts around 30 – 60 minutes and it’s still relatively light. Think of this as the stage that you would want to wake up right after if you are having a “power nap”. That’s because your body is preparing for deep sleep and your muscles relax even further. Additionally, your heart rate continues to slow down as your temperature also drops. You will spend the most time in this stage than any other throughout the night.

Stage 3:

Now you’re getting into deep sleep territory, lasting around 20 – 40 minutes. Your brain will begin to process “slow waves”. While you’re not yet dreaming, your muscles are very relaxed and it’s harder for you to wake up. This is the time when your body is repairing muscles, boosting immune function and restoring energy.

What is happening during REM sleep? 

Now we’re at the climax, the state of dreaming. And lucky for us, in an average night, we can have five to six REM cycles alone. In this final stage, your brain becomes more active, your eyes will move rapidly (hence rapid eye movement) behind closed lids and brain waves will somewhat mimic waves similar to those during waking hours. The body will be in a paralyzed state while your heart rate and blood pressure increases.

series of woman in various sleeping poses

How long is a full sleep cycle?

Generally one sleep cycle that goes through the above four stages will last around 90 minutes. So if you get 7 hours of sleep per night on average, you’ll cycle through the stages four to five times. But as the night progresses, the amount of time we spend in each stage changes.

For the first 2-3 times that you go through a sleep cycle, you spend most of your time in stage 3 of Non-REM sleep. Then during the final 2-3 cycles, you’ll spend more time in REM as each subsequent REM stage gets longer as the night goes on. Some may wish to lengthen their REM sleep for increased sleep efficiency, check out how to do that here.

How your sleep cycle changes with age

As we age, we don’t just grow taller; our sleep patterns develop as well. Overall, the amount of time we spend each day sleeping decreases, but there’s even more to it. Our age is also an indicator for the quality of sleep we get. Take newborns – they spend at least half of their total sleep in REM sleep, but as soon as they hit 2 years old, that drops to a quarter of total sleep spent in REM. 

Then as we continue to age, especially from childhood to adulthood, we lose the amount of deep sleep (Non-REM Stage 3) and REM sleep we get and it’s instead replaced with more of Stage 2 in Non-REM sleep. As such, a big effect of aging is that our sleep becomes lighter. After all, it’s much harder to wake up a sleeping child than it is an adult.

Why you need sleep

Once you understand your sleep cycle more, you can better appreciate how much sleep impacts our brain and bodily function. Sleep, and each stage of it, plays a vital role in healthy brain function, emotional well-being, physical health, daytime performance and safety. To improve your unavoidable daily (or nightly) event, follow these 8 tips to sleep better.