A lot happens in your body while you sleep including your REM and non-REM cycle.
REM stands for rapid eye movement, and during REM sleep your eyes move around rapidly in a range of directions, but don’t send any visual information to your brain.
In your sleep cycle non-REM sleep comes first, followed by a shorter period of REM sleep, and then the cycle starts over again. Dreams typically happen during REM sleep.
What happens during non-REM sleep?
There are three phases of non-REM sleep. Each stage can last between 5 and 15 minutes. You go through all three phases before reaching REM sleep.
Stage one is where your eyes are closed, but it’s easy to wake up. This phase may last for 5 to 10 minutes.
Stage two happens when you are in light sleep. Your heart rate slows, and your body temperature drops. Your body is getting ready for deep sleep. This can last for 10 to 25 minutes.
Stage three is the deep sleep stage. It’s harder to rouse you during this stage, and if someone woke you up, you would feel disoriented for a few minutes.
During the deep stages of non-REM sleep, the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system.
As you get older, you sleep more lightly and get less deep sleep. Aging is also linked to shorter time spans of sleep, although studies show you still need as much sleep as when you were younger.
What happens during REM sleep?
Usually, REM sleep happens 90 minutes after you fall asleep. The first period of REM typically lasts 10 minutes. Each of your later REM stages gets longer, and the final one may last up to an hour. Your heart rate and breathing quickens.
You can have intense dreams during REM sleep, since your brain is more active. REM is important because it stimulates the areas of the brain that help with learning and is associated with increased production of proteins.