Stages Of Sleep & Sleep Cycles
Ever wonder why at times you wake up feeling refreshed while at other times you wake up still longing for a few minutes more, despite sleeping for relatively the same amount of time? Could it be that you’re roused from a specific part or stage of sleep? There are five known stages in the sleep cycle. What are the five stages of sleep? And since there are stages, what is the deepest stage of sleep? How long is each sleep stage? What happens during each sleep stage?
Non-REM and REM Sleep Cycles
Before we get to the stages of the sleep cycle, we first identify the two types of sleep. NREM and REM. NREM stands for Non-Rapid Eye Movement while REM stands for Rapid Eye Movement sleep. These are distinguished by the rapid eye movement a sleeper makes while sleeping.
REM sleep is where dreams occur where we either live in a fantasy world or exist in a world similar to ours, acting out moments of our past or future. Our eyes move rapidly under the closed eyelids as if seeing the dream world, hence the term. NREM sleep can be divided into four stages, where the last stage is REM sleep. Below are the five stages of sleep describing
What happens during each sleep stage?
- Stage 1 – is the beginning of the sleep cycle, the first stage of NREM sleep. This is where the person is in a very light sleep, which can easily be awakened by external stimuli. This stage lasts between one to ten minutes. Breathing begins to slow down, the muscles relax, and the heartbeat becomes regular. The eyes also roll back, and the eyelids close or remain partially open. Hypnic jerking and twitching can happen, especially when a sleep-deprived person tries to fight off the onset of sleep. A person may also feel something similar to falling. Once dozed off, the body’s blood pressure decreases, and the brain’s temperature also decreases as brain activity decreases. Persons often wake up startled during this stage after a simple tap from a colleague at work. This stage is also known as very light sleep.
- Stage 2 – is a deeper stage of sleep which differs from Stage 1 due to slow heart rate and lower body temperature. Rousing a person at this stage is more complicated. All other bodily functions slow down. Blood pressure lowers and monitored brainwaves become larger. Stage 2 is another term for light sleep. This stage lasts for about 20 minutes.
- Stage 3 – When a person sleeps like a log, he/she is likely in stage 3 or 4. This phase of the five stages of sleep happens about 35 to 45 minutes in. Stage 3 is the beginning of what is known as deep sleep or delta sleep, which describes a person’s brainwaves when running through an n EEG (electroencephalogram). During this stage, people are difficult to wake up despite loud noises and light stimulus. And when people are woken up during this stage, they appear disoriented.
What is the deepest stage of sleep?
- Stage 4 – This is the deepest stage of sleep, otherwise known as very deep sleep. Breathing at this last stage of NREM sleep is rhythmic, and there is very little muscle activity. As in the previous stage, the brain produces delta waves when seen through an EEG. Stage 3 and four is also where the body restores itself, heal any injuries, and promotes growth in young individuals. The brain also refreshes itself for the next-day grind. Sleepwalking and night terrors also occur at this stage.
- Stage 5 – Speaking of night terrors, they are different from nightmares hat happen during stage 5 or REM sleep. Night terrors are an instinctive feeling of fear where persons suddenly bolt up during deep sleep. While nightmares are induced fear due to frightful experiences while dreaming. Stage 5 is where dreaming occurs and is named after the rapid eye movements observed under a sleeping person’s closed eyelids. The brain waves are active at this stage, processing what the person sees and experiences during dreams.
It’s easy to wake an individual during this stage compared to Stage 3 or 4. But like Stage 3 and 4, a person can feel groggy when awakened from REM sleep. Body restoration also continues during REM sleep. But why dream at all and disrupt what is already a pristine stage 3 and 4? We complain that we do not have enough waking hours or wonder why we need to sleep so long, or at all since life is so short as it is.
Scientists believe that dreaming is essential to brain development, especially in children. The body needs to rest and restore itself but to compensate, dreams are used to simulate additional waking hours for the body from which we can learn literally or figuratively.
Are There 4 or 5 Stages of Sleep?
Other sources state that there are only four stages of sleep. So are there 4 or 5 stages of sleep? Both are true, but many cite the simplified version of combining stage 3 and 4. So the four stages of the sleep cycle can be summarized as very light sleep, light sleep, deep sleep, and REM sleep.
The Sleep Cycle
But humans do not experience the 4 or 5 stages of sleep in one go during a sleep session. Each sleep cycle lasts from 90 to 120 minutes. That’s about four cycles for a standard 8-hour period. These sleep cycles don’t tend to be sequential either, nor are they completed all the time. There are times that persons only sleep at stages one to two, rinse and repeat and only manage to reach stage 3 and REM into the deep hours of the night.
So although a person gets to sleep 8 hours a night regularly, waking up may not be the same every day as many factors can affect or disrupt the normal sleep cycle and the amount of deep sleep (stage 3 and 4) the human body requires. Thus there are days when a person feels exhausted despite sleeping for 8 hours or feel refreshed after sleeping for 6 or 7.
The fact that we can’t make up our minds on how many stages of sleep there are or whether or not to classify REM sleep as part of the sleep cycle means that there are parts or this regular but essential human activity that remain a mystery. AT this stage, however, we understand enough that as adults, obtaining the right amount of sleep is necessary to heal the body and restore its strength in preparation for the next day.