Have you ever wondered what actually happens when you fall asleep? Why do you dream, and why do they seem to disappear before you can properly remember them? Why do we sometimes sleepwalk, and what’s that crazy falling sensation we all get? Today, we’re going to answer all of those questions and more, as we dive into the science and stages of sleep.

A good night’s sleep leaves us feeling rested and recharged. It helps keep our digestive systems moving, and restores our energy levels. On average, we need between 7-8 hours sleep every night. Though that number is much higher for teenagers (they’re not just being lazy!) It’s even higher than that for babies and toddlers. But, why do we need so much sleep, and what happens when we close our eyes?

Well, the science behind it seems to suggest there are four simple stages that repeat themselves roughly every 90 minutes. Stages 1-4 takes you from lightest sleep to deepest. Interspersing this cycle are regular periods of REM sleep, which is where most of our dreams happen. If you’re already intrigued, keep reading to find out more.

Stage 1 (Light sleep)

Stage 1 occurs just as you start to doze off. You begin to drift in and out of sleep, but it’s still very easy to wake you. Our muscles begin to relax, which is why they often feel like they’re spasming at this stage. It’s in this part of the sleep cycle where you’ll often feel that falling sensation. It’s a simple muscle spasm that draws you back to reality. If you wake up right at the start of this cycle, you’ll usually feel refreshed and ready to go! That’s why so many people try to time their sleep cycles just right.

Stage 2

Stage 2 is sort of a transition state. Your body is now fully asleep, and starting to move towards the deeper levels of unconscious. Your heart rate slows down, your eyes stop moving, and your brain waves get long and slow. Your body temperature also begins to drop, as you prepare for that lovely deep sleep!

Stage 3 & 4 (Deep sleep)

In stage 3, your brain starts to produce extremely long and slow waves, called delta waves. They are still interspersed with one or two faster waves. But, on the whole, you have now entered deep sleep. Most sleep scientists now consider stage 3 and 4 as the same thing.

Stage 4 is the deepest, most restorative part of the sleep cycle. It’s in this period that your muscles begin to repair themselves. There is lots of tissue growth as your body gets to work. Your energy levels can now be restored, and are topped back up. Your body also releases growth hormones during stages 3 and 4. This is particularly important for children and teens, who are still building muscle and developing bone structure.

Stage 4 is particularly interesting, because it’s where some of the strangest sleep phenomena happens. It’s during this period that we’ll often find ourselves sleepwalking. It’s also when children will wet the bed. Most terrifyingly, it’s usually when sleep-terrors strike. And, because we’re in such a deep sleep, it’s very, very difficult to wake up during this part of the cycle.

If you do wake up during this part of the cycle, you’ll feel incredibly groggy and confused. Your brain is operating at a much slower rate, and your muscles are not yet back to full function.

REM (Rapid eye movement)

The cycle is punctuated by three or four periods of REM sleep. At this point, our brain is back in fully-active mode. It operates as it would during the day. That’s why the REM stage is where we start dreaming. Or at least, where we remember our dreams. Your eyes dart back and forth, and your blood pressure rises again. The length of the REM stages increase as the night goes on. Hence why we seem to remember the dreams right before we wake up.

One of the intriguing things about the REM stage is that our muscles are almost completely paralysed. They’re in a state of complete relaxation while the body slowly wakes back up. It’s lead to what scientists call ‘sleep paralysis’. If you wake during this period of sleep, you’ll often feel like you’re unable to move your limbs. If it happens during a nightmare, it can be terrifying. With a natural sleep cycle, you should wake just after the REM stage completes. You’ll feel refreshed and revitalised thank to lots of lovely stage 4 snoozing! Now you know what’s going on when you close your eyes at night.