Sleep is one of the most important things we need to take care of in order to live a healthy life and have enough energy to do all the activities we want to do on a daily basis.
When discussing sleep, the first thing we need to learn is that the idea that sleep is just one long state that we enter every night is a false one. Our sleep time is actually broken down into what are called sleep cycles.
Each sleep cycle is around 90 minutes long. There is some variation here between 70 and 110 minutes, but 90 minutes is a good figure to keep in mind as a start.
During the night, sleeping follows a predictable pattern, moving back and forth between two different types of sleep.
These two main types of sleep are referred to as non-rapid-eye-movement (NREM) and rapid-eye-movement (REM) sleep. On an electroencephalogram (EEG), REM sleep, often called “active sleep,” is identifiable by its characteristic low-amplitude (small), high-frequency (fast) waves and alpha rhythm, as well as the eye movements for which it is named.
Many sleep experts think that these eye movements are in some way related to dreams. REM sleep comprises about 20 to 25 percent of total sleep in typical healthy adults. The average length of the first NREM-REM sleep cycle is between 70 and 100 minutes; the average length of the second and later cycles is about 90 to 120 minutes.