Sleep Phases
Why REM is More Than a Rock BandEach night the body goes through several different phases: Light sleep, Deep sleep, REM sleep, and Wakefulness. These sleep phases go through 3-6 cycles each night. The transitions between each of the phases are gradual and not always easy to remember or detect.
What are Sleep Phases?
During the night, the mind and body go through many changes that involve going through a very predictable and regular pattern of sleep phases. The different phases of sleep are Light sleep, Deep sleep and REM sleep. These sleep phases are often interrupted during the night by wakefulness – that is, Disrupted sleep. Light sleep accounts for about half of the night and bridges the gap between the other sleep phases. Deep and REM sleep are the two (very different) components of Restorative sleep, the times during the night when the body undergoes the most mental and physical restoration.
REM, Light and Deep Sleep
A sleep cycle is a period during the night in which you go through each of the sleep phases, and perhaps some wakefulness. A typical sleep cycle involves: going into Light sleep, which deepens and can become Deep sleep, especially earlier in the night, then back into Light sleep which then transitions into REM sleep. It is very common to wake up either as you enter or exit REM sleep while transitioning out of or into Light sleep. This is the most natural time to wake up and can occur during any of the usual 3-6 sleep cycles over the course of a night. Notice that the body does not simply go into a sleep which just gets deeper and deeper over the course of the night until you wake up. Sleep deepens and lightens several times over the course of a night and waking up is often a normal part of this natural process.
The transitions between the different sleep phases are usually very fluid and can occur over the course of several minutes. This is also the case when transitioning into and out of wakefulness. It is very difficult to pinpoint the exact point at which you fell asleep or woke up in large part because falling asleep and waking up do not happen with the flip of a switch. It is common to wake up out of Light sleep without even realizing you were asleep, especially if you are doing something other than trying to fall asleep – such as watching TV or driving (drowsy driving is very dangerous and should be avoided). It is also possible to forget that you have woken up during the night. Have you ever had the experience of turning off your alarm in the morning, going back to sleep, and then having no recollection of having woken up to turn off your alarm? This is because short-term memory turns off as you drift into one of the sleep phases.