While you sleep, you go through a cycle of sleep phases. The first phase is light sleep, followed by deep sleep. A full sleep cycle can last about 90 minutes and is normally repeated several times each night. Our sleep state alternates between rapid eye movement (REM) and other states (collectively referred to as non-REM)
Please note that the Sleep Cycle app does not track using these sleep stages, we use Deep sleep, Sleep, and Awake.
Sleep Cycles
Sleep cycles are regularly occurring patterns of brain waves which occur while we sleep. Sleep cycles typically last around ninety minutes, during which time the brain cycles from slow-wave sleep to REM sleep in which we experience dreams.
Since sleep cycles occur regularly every ninety minutes or so, the average individual experiences around four to six sleep cycles in a full seven to nine-hour night of sleep. The need to schedule specific wake up times is important to ensure the brain wakes up at an appropriate stage in its sleep cycle to ensure we wake up refreshed.
As Sleep Cycle can detect your light sleep phase, the Smart Alarm will gently wake users up in their lightest sleep phase.
Non-REM
Non-REM sleep is divided into three stages. The first two stages account for light sleep, the third is deep sleep. You can see these stages in your sleep analysis.
For the typical person, it takes about 45 minutes to slip through the first two stages into the last. In these stages most physiological processes are greatly reduced. It’s very difficult to wake a person in deep sleep and nightmares can occur during this time as well. Waking up at this stage can result in a disorientated and groggy feeling (which is called sleep inertia).
REM
After about 90 minutes, we enter REM sleep in which brain activity changes dramatically. Our muscles become inhibited but our eyes start flickering, hence Rapid Eye Movement.
In fact, brain activity is said to be more intense in REM than when we are awake. Most dreaming also occurs in REM. The muscle paralysis keeps us from acting out our dreams, even though our eyes move according to what we see in our dreams. To be able to track REM sleep accurately, you need to track eye movements - tracking this stage is best done in a sleep lab and clinical setting.
Non-REM sleep is believed to help the brain’s physiological processes reboot, while REM is believed to help us work through psychological needs.
Recent research indicates that REM sleep is necessary for processing new information, i.e. learning. Early in life we spend about 50% of our sleep in REM. But from about the age of 10 we stabilize at about 25%.
When we are sleep deprived we spend more time in non-REM, verifying our body’s need to “reboot”. This also means less time spent in REM sleep, can lead to irritability and mood swings.