What exactly happens while we sleep? We spend about one-third of our life sleeping—or at least attempting to do so—yet we are not usually aware of what is going on in our minds and bodies during that time.
Luckily, years of scientific research have provided us with insight into the fascinating processes happening beneath our level of awareness while we sleep, and we now understand that sleep occurs in stages. Here, we will go over each of these stages of sleep, especially focusing on the importance of REM sleep, the part of the cycle where dreaming occurs. We will also identify some signs that you are—or are not—getting the quality sleep you need.
Stages of Sleep
The stages of sleep are divided into two types: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. The stages collectively make a sleep cycle, which lasts about 90 to 110 minutes and is repeated throughout the night.
NREM Stage 1
The first stage of NREM sleep is the shortest stage, lasting from about one to five minutes. In this stage, the brain and body start to slow down, but the body hasn’t fully relaxed. It’s common for the body to twitch, and the person can easily be woken up during this stage.
NREM Stage 2
More substantial changes begin to occur in the second stage of NREM sleep. Body temperature drops, muscles relax, and breathing and heart rate slow down. Brain activity also slows, except for short bursts of activity, which help protect the body from being woken up by outside stimuli.
During the first sleep cycle of the night, this stage lasts about 10 to 25 minutes, and the length of this stage progressively increases for each sleep cycle throughout the night. When it averages out, a person generally spends about half their sleep time in NREM stage 2.
NREM Stage 3
During this stage, a person is in a deep sleep that is difficult to be awoken from. The body’s muscles relax even more, and breathing and heart rate further decrease. Brain activity transitions to a pattern identified by delta waves, which are the slowest brain waves.
This is the restorative stage in which the body repairs itself, including muscle recovery and processes for proper immune function, and the brain processes information and consolidates memories. This stage usually lasts for 20 to 40 minutes, and people spend the most time in this stage during the first half of the night, while it gets replaced later in the night with more REM sleep.
After the third stage of NREM sleep, the body enters NREM Stage 2 once more before transitioning to REM sleep.
Although body muscles are temporarily paralyzed during REM sleep, except for the muscles that control breathing and eye movement, the brain is highly active, similar to activity levels during waking hours. In this stage, a person’s eyes move rapidly beneath closed eyelids, hence why it is called rapid eye movement sleep.
REM sleep is important for cognitive functions, such as memory, learning, and creativity. It is also the period of sleep with the most vivid dreams. People usually enter REM sleep after about 90 minutes of being asleep, and while the first stage may only last a few minutes, REM stages get longer as the night goes on, lasting for around an hour in later stages. Most people spend about a quarter of their sleep time in REM sleep.
The Importance of REM Sleep and Dreaming
As mentioned, REM sleep plays a large part in healthy cognitive functioning. It is also the stage of sleep with the most vivid dreams. But is there anything inherently beneficial about dreams? While researchers have differing opinions on the function of dreams, commonly held theories posit that dreaming aids in processing emotions, preparing to deal with threats, thinking creatively, and storing important memories.
Since most dreaming occurs during the deep stages of REM sleep, sleep conditions that disrupt your sleep cycles, such as sleep apnea, will likewise affect your dreams. Sleep apnea is a sleep disorder in which breathing repeatedly stops and starts while you sleep, often causing a person to wake multiple times throughout the night and leading to symptoms like snoring, impaired cognitive functioning, and excessive daytime fatigue.
So, is “not dreaming” a sign of a condition, such as sleep apnea? While failure to recall your dreams does not necessarily mean you aren’t dreaming, it is possible that is the case, which could be a result of sleep apnea. A study found that while 71.4 percent of those without sleep apnea could remember their dreams, only 43.2 percent with sleep apnea could remember them.
Further, sleep apnea is associated with higher rates of nightmares, since those with sleep apnea may be suffering from a lack of oxygen while they are dreaming.
There are many factors that can affect the quality of sleep and dreams, including health conditions, pregnancy, mental disorders, foods, and daily activities. But, if you have a hard time recalling your dreams when you wake and experience other symptoms of sleep apnea, you might want to consider asking a medical professional about getting screened for the condition.
Whether or not we understand exactly what our minds do while we dream, we know that quality REM sleep is crucial to many important bodily and mental processes. It’s important to understand these basics of the sleep cycle so we can prioritize getting a good amount of sleep each night and experiencing optimal physical and mental health.
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