It’s easy to think that there’s not much going on while you’re in bed. After all, sleeping people tend to look pretty peaceful, right? They may move or talk some, but it’s not very often and almost never purposeful or meaningful.
However, there’s a lot more going on than meets the eye when it comes to sleep. The brain actually moves through several different, discernable stages while you sleep. These each have different characteristics which, while not visible to the average person, become readily apparent when a person is hooked up to scientific measuring devices while they sleep.
We cycle through 4 stages of non-REM sleep and one stage of REM sleep several times every night. You may not know it, but your body is busy even when your mind is turned off.
Stage 1 sleep is actually the act of falling asleep. You may feel extremely sleepy like you can’t possibly keep your eyes open for another minute. You may also feel like you drift in and out of sleep for a while. If someone wakes you up while you’re in this stage, you may not think that you got any rest at all.
However, Stage 1 is where your body begins to prepare for deeper sleep. Your brain waves begin to slow, though they still look much like they did when you were awake. The heart and the breathing rate both go down. You still have some eye movement, but not like you did when you were awake.
If you’ve ever jerked yourself awake thinking you were falling, you were in Stage 1 sleep. This happens because your muscles are still active during this stage, and sometimes they all contract together.
It’s hard to find the exact line between Stage 1 and Stage 2 sleep, but Stage 2 usually comes about 10 minutes after the onset of Stage 1. In this sleep, your brain waves get even longer and more spread out, though these long wave patterns are interspersed with flurries of activity.
We actually spend most of our time in Stage 2 sleep, as we cycle through it numerous times throughout the course of the night. As people get older, they spend more and more time in this stage, with less time spent in REM sleep.
During Stage 2, your heart and lungs will get even more of a rest, as their rates slow even more. Eye movement ceases here, and muscle contractions become fewer and farther between. It’s still pretty easy to wake up from Stage 2 sleep, but not as easy as it was in Stage 1.
This is the first stage of deep sleep. Your brain begins to produce delta waves, which are the slowest ones it has. These are, however, interrupted by shorter waves, which disappear as you sleep deeper and deeper.
Stage 3 sleepers are incredibly difficult to wake. In fact, they may not notice noises up to 100 decibels. Most people are so deeply asleep in Stage 3 that you have to shake them or touch them to wake them up. When they do wake up, they tend to be groggy, disoriented, or confused.
Stage 3 sleep is where some sleep disturbances begin. People who sleepwalk, talk in their sleep, struggle with wetting the bed, or have night terrors tend to have them during Stage 3 or Stage 4 sleep.
Stage 4 is basically a deeper extension of Stage 3. The biggest difference between the two is that Stage 4 is characterized exclusively by long, slow delta waves in the brain. During this stage, the body is as slowed down as it ever gets. Both breathing and heart rates are significantly different from what they are during the day. People who struggle with the sleep disturbances mentioned above often experience them as they transition from Stage 4 into REM sleep.
REM sleep is where dreams happen. It’s also where your body seems to wake up without actually waking up. Your brain waves appear almost as they do while you’re awake, and your heart and breathing rates pick up, too, Your eyes start to move again, possibly coinciding with the images in your dreams.
The biggest difference between REM sleep and being awake is that your muscles are paralyzed. This may be a good thing, as it keeps you from acting out your dreams!
All of this sets REM apart from the other sleep stages. It is unique, and scientists aren’t entirely sure why.
The more we learn about sleep, the more fascinating the study becomes. There’s still so much we don’t know about why our brain waves change when we sleep, how sleep came to be, and what our brains are doing while we sleep. Hopefully, researchers will be able to answer these questions soon.