You know that feeling when you’ve had a bad night’s sleep, and you can’t seem to function? Or when you have a brilliant night’s sleep and feel like you could conquer the world? Well, it turns out some pretty cool things are happening in your body while you snooze. We give a brief overview of what happens during REM and non-REM sleep (both key parts of a healthy sleep cycle), as well as how body temperature, breathing, heart rate and brain activity change throughout each phase.
Body temperature, breathing, heart rate and brain activity
As you fall deeply asleep, your body temperature drops. It's thought that this is to conserve heat and energy by keeping the body cool. This can be easily seen if you were to put an ear to someone's head as they sleep—you'd hear it become slower and more regular as they drift into non-REM sleep. As we progress deeper into the stage, breathing becomes slower and more regular, too (this is why snoring can sometimes occur during deep sleep).
When you are in REM (rapid eye movement) sleep, which happens every 90 minutes or so throughout the night, your brain activity increases dramatically compared with when you're awake or in non-REM sleep. Your eyes move around rapidly beneath their lids, and all kinds of crazy stuff happen inside your brain cells!
Heart rate also decreases when we enter deep stages of sleep; however, there are some interesting anomalies here, too: Studies have shown that heart rate actually increases slightly as we enter into REM! This may seem strange, but it makes sense: When we dream during REM, our brain activity is similar to when we're awake—so perhaps this slight increase in heart rate helps us stay alert during dreams?
Sleep Cycles
When you sleep, you go through multiple periods of Non-REM (rapid eye movement) and REM (rapid eye movement) sleep. Each cycle lasts between 60 and 90 minutes, with the first cycle being the longest.
These cycles are split into two types: non-REM and REM.
- During a typical night's sleep, you'll move through four to six non-REM cycles before entering a REM period. Each cycle consists of three stages: N1 (light sleep), N2 (lighter than stage 1 but still fairly deep), and N3 (deepest stage).
- During each subsequent non-REM cycle, you spend less time in stage 3—and more time in stage 2 or even light sleep—until finally reaching an almost pure state of light sleep for about 20 minutes before beginning another cycle through stages 1–3 again.
Non REM Sleep
Non-REM sleep is divided into three stages:
- Stage 1 (shallowest) - where your body and brain activity slows down. It usually lasts for about 5 minutes.
- Stage 2 (medium depth) - where you'll drift in and out of being awake and asleep, feeling relaxed with slower brain waves than during wakefulness. This stage can last anywhere from 10 to 25 minutes, depending on how tired you are when you go to bed.
- Stage 3 (deepest) - where your body completely relaxes while the heart rate slows down, breathing becomes more regular, and blood pressure drops slightly as it prepares itself for REM sleep.
REM Sleep
REM sleep, or rapid eye movement sleep, is the stage of the sleep cycle in which dreaming occurs. During REM sleep, the brain is active, but your body remains still. This is because it takes less energy for you to maintain your posture during this time than when you're awake. Brain activity during REM sleep is similar to that of when you're awake—which means that it's believed to be essential for enabling brain functions like learning and memory.
REM usually begins about 90 minutes into your sleep cycle and lasts for about 20 minutes at first. As the night progresses, however, people tend to spend more time in REM (and overall less time in deep or slow-wave stages).
We've learned a lot about sleep, but there's still so much we don't know. While there is some evidence that sleep can help you feel less tired and perform better in certain tasks, it's also important to remember that not getting enough sleep can have negative effects on your health and well-being.