The Mysterious Process of Sleep
The slumber many of us take for granted isn’t just a passive state that lets the body recharge its batteries. Rather, it’s a time of intense activity, when muscles repair themselves, brain waves slow down, memories are formed, hormones are released and growth and healing occur. Sleep is critical for the body, and studies have shown that people who don’t get enough of it may suffer from a variety of physical and mental problems, including obesity, diabetes, heart disease and depression.
Sleep experts haven’t yet agreed on exactly why humans need to sleep, but they do know that it serves an important function. One theory is that it allows the body to “reboot” the immune system, clearing away cellular and protein debris that builds up during the day. This is why getting enough restful sleep is so crucial for maintaining a healthy, functioning immune system.
Another possible reason for sleep is that it helps to reinforce our memory, converting short-term memories into longer-lasting ones. That’s why it’s important to remember to make time for good quality sleep each night, especially in the hours leading up to bedtime.
A growing body of evidence shows that sleep plays a role in keeping the mind sharp, learning and remembering. It also supports emotional stability and can help prevent health problems such as heart disease and stroke.
It wasn’t always clear what happened during sleep, but in the past few decades, scientists have learned a great deal about this mysterious process. They have identified four distinct stages of sleep that repeat several times throughout the night.
The first stage of sleep is characterized by light eye movements and a general feeling of drowsiness. You may even experience hypnagogic jerks, which are the little twitches that you sometimes feel just before falling asleep. This phase of sleep is referred to as stage 1 and usually lasts only a few minutes.
Once you’ve entered stage 2, your brain waves begin to slow down and your breathing and heart rate slow as well. It’s in this phase that dreams usually take place, and they can seem very real. In fact, dreams often mirror the events of our waking lives. This is why some people choose to keep a sleep journal, or use a technique called dream recollection to try to increase their lucidity.
During the third and final stage of sleep, or deep sleep, your brain waves become very slow and synchronized. This is when your body repairs itself, and it’s during this period that most of the growth and healing occurs. The glymphatic system, which clears waste from the brain, is particularly active during this time.
You cycle through non-REM and REM sleep for different lengths of time several times during a typical night, but you spend more time in REM as the night progresses. It takes an average of 70 to 120 minutes to complete a sleep cycle. REM sleep typically makes up about 20% of the total sleep time.