While you were sleeping:
Scientists used to think that people were physically and mentally inactive during sleep. But now they know that’s not the case. All night long, your body and brain do quite a bit of work that’s key for your health. There are two main types of sleep that we cycle in and out of when we rest -- REM (rapid eye movement) and non-REM sleep.
You begin the night in non-REM sleep and spend most of your rest time there. It starts light, in the “N1” stage, and moves to the deep “N3” stage. During this progression, your brain becomes less responsive to the outside world, and it gets harder to wake up. Your thoughts and most body functions slow down. You spend about half a normal night’s sleep in the “N2” phase, when scientists think you file away long-term memories.
REM Stage -This stage got its name because of the way your eyes dart back and forth behind your lids. You dream most in this stage. Your pulse, body temperature, breathing, and blood pressure rise to daytime levels. Your sympathetic nervous system, which helps with automatic responses like “fight or flight,” gets very active. And yet your body stays almost completely still.
You typically go through all the sleep stages three to five times a night. The first REM stage may be just a few minutes, but gets longer with each new cycle, up to about a half an hour. The N3 stage, on the other hand, tends to get shorter with each new cycle. And if you lose REM sleep for whatever reason, your body will try to make it up the next night. Scientists aren’t sure of the purpose of any of this.
Body Temperature- It drops a couple of degrees as you get drowsy before bed and is lowest about 2 hours before you wake up. In REM sleep, your brain even turns off your body thermometer. That’s when heat or cold in your bedroom affects you more. In general, a cooler room helps you sleep better. A few pushups or a jog when you wake raises your temperature and makes you more alert.
Breathing- It changes a lot when you’re awake, of course. But as you fall deeply asleep, you breathe more slowly and in a more regular pattern. Then, as you enter the REM stage, your breathing gets faster and varies more.
Heart Rate -Deep, non-REM sleep lowers your pulse and blood pressure, which gives your heart and blood vessels a chance to rest and recover. But during REM, these rates go back up or change around.