Sleep is a necessity for the majority of advanced organisms, including humans. Due to the circadian rhythm (also known as the body clock) and evolutionary processes, human beings usually rest at night. Although we sleep every night, our quality of sleep can fluctuate from night-to-night.
Some nights we have strange, vivid dreams. But sometimes we can also go for weeks without being able to recall a single one. Other times, even if we spend long hours sleeping, we wake up feeling more tired than before going to bed.
Why is it so hard to fall asleep or to wake up at times? What are the causes of unpleasant sleep-related experiences, such as night terrors or sleepwalking? How much total sleep time do we really need? These are only a few questions that we might have related to the familiar, yet puzzling, topic of sleep.
In this article, we compiled key information about sleep, focusing on different stages and the influence they have on our overall quality of sleep. It’s very important to understand how sleep works and how to make the most of it. Then, we will be able to improve our physical and mental well-being, as well as our performance in everyday challenges.
Difference between REM and non-REM sleep
Throughout the night you experience a cycle of two types of sleep known as non-REM and REM (rapid eye movement) sleep.
REM sleep is characterized by low and fast patterns of brain waves and rapid eye movement (by which it is named). REM sleep is often called “active sleep”. During this phase, the brain can be even more active than when you are awake. Increased brain activity is closely related to vivid dreaming. This is another attribute distinctive to REM sleep.
Non-REM sleep is referred to as “quiet sleep”. The brain waves become gradually slower and our muscles relax. This sleep can be further divided into 3 stages: a transition from being awake, light, and deep sleep. Deep sleep is an incredibly important stage as it rejuvenates your body.
Stages of Sleep
Before you go to sleep, you are in a wakeful state of consciousness. If your brain would be measured with EEG you could see that during this phase the Alpha and Beta brain waves are both active and more dominant.
Once you start drifting off, your body enters the non-REM sleep. Non-REM sleep is separated into three stages. They’re known as N1, N2, and N3, and they happen before we reach REM sleep. Each stage is characterized by the patterns of brain waves and the effects on your body and mind.
Stage N1 – Relaxed Wakefulness
This stage is a transition between wakefulness and sleep. This is a relatively light form of sleep lasting 5 to 10 minutes. During this time, your body temperature slightly decreases, body muscles relax, and your heart rate, breathing, and eye movement slow down.
Stage one (N1) of sleep is very easy to be woken up from—even the slightest disturbance can bring you back to consciousness. If you wake up during this time, you might not even realize you were asleep in the first place.
During this phase, hypnagogic jerks are a common phenomenon. These are a sudden involuntary contraction of a muscle. Some people describe it as a “jump” sensation, while others refer to it as “falling”. It can startle you and prevent you from falling asleep.
Despite being responsible for relaxation, Alpha brain waves can also make you experience sensations, such as hearing sounds that are not there. While these mild auditory hallucinations might make a person uneasy, they are quite rare and completely harmless. At the end of the N1 sleep stage, Theta brainwaves begin and you enter the second stage of slightly deeper sleep.
Stage N2 – Light Sleep
As you enter Stage two, your K-complexes activate. K-complexes respond to environmental stimulation. They protect your sleeping brain by evaluating false danger, allowing you to go into deeper stages of sleep without disturbance.
Stage two (N2) is considered a light sleep that lasts about 30 to 60 minutes. In a night’s span, your body will spend the most amount of time in Stage two. During this stage, your body temperature drops and your heart rate slows down. You also find your muscles relax even further.
In the course of this period, you experience sleep spindles. These are bursts of brain waves that produce rapid and dynamic brain activity. Researchers believe sleep spindles correlate with memory and better performance during the day.
Stage N3 – Deep Sleep
As you enter the third stage of sleep, Beta brainwaves take place. Stage three lasts 20 to 40 minutes. At the N3 sleep stage, your body temperature and blood pressure drop even lower. Your heart rate and breathing reach its slowest state and muscle activity ceases; this results in your body becoming immobilized and eye movement stopping.
Deep sleep is important as it releases hormones that rejuvenate your body and strengthen your immune system. Your muscles, as well as tissues, get restored.
At this sleep stage, it’s hard to wake up. And if you do, you feel very disoriented. For this reason, you might want to rethink the duration of your naptime. Taking a nap longer than half an hour means you could be waking up in a deep stage of sleep—leaving you more tired than you were before you dozed off.
Parasomnias also occur during Stage three. In this stage, sleepwalking, sleeptalking, and night terrors are pretty common. These disorders trigger the activation of your vegetative nervous and motion systems. They can also happen during the process of sleep-wake transitions, as your muscles still have the ability to function.
After going through the first three stages, REM sleep occurs. The first stage of REM lasts around 10 minutes, and each time you enter REM, the stage gets a little longer. During this sleep phase, the brain is bursting with activity. During this stage, your heart rate and blood pressure increase, your body temperature falls to its lowest point, and your breathing intensifies and becomes irregular. This is the state when your eyes and eyelids flutter.
REM sleep is when your brain is the most active and the most vivid dreams occur. To prevent you from acting out your dreams while you are asleep, your brain temporarily paralyzes your muscles in the arms and legs. No voluntary muscle movements are possible because motor neurons are not stimulated. This phenomenon is known as REM atonia. REM sleep is also seen as a “paradoxical sleep”. This is because your brain activity is so high but your muscles are still and not responsive.
Just like non-REM sleep, REM sleep also stimulates areas of our brain related to successive learning and memory retention. Studies have shown that people learning a new physical task will improve their performance overnight. But only as long as they get enough REM sleep.
Sleepers usually awaken at the end of REM sleep and sometimes during the REM. But these days many people rely on alarms, which wake you at a desired time of day regardless of your stage of sleep.
When Do You Dream
Just because you might not remember what you have dreamt of doesn’t mean you don’t dream at all. As mentioned before, while there’s a possibility to experience dreams at all sleep stages, most of them vividly occur during REM sleep.
Some factors that you deal with throughout the day may influence your dreams. It’s very common to find details in your dreams from real-life experiences. Or to dream about the concerns you have been having. Dr. Rosalind Cartwright, Professor and Chairman of the Department of Psychology at Rush University Medical Center, theorized that during dreams, our brain incorporates memories, solves problems, and sorts through complicated thoughts and feelings.
But this is only a theory. The real reason behind dreaming is still unknown.
What Is a Sleep Cycle?
After you drift off, you progress through each stage of sleep, completing a full sleep cycle after completing Stage one through REM. A full sleep cycle can take 90 to 110 minutes to complete, and you typically undergo five sleep cycles in a typical night.
During the first half of your sleep, the duration of deep sleep is longer. But as the night progresses, REM sleep increases with each cycle. This is especially noticeable before natural awakening.
Understanding how sleep cycles work is important to maintaining a healthy body and mind. A healthy person should undergo about 35 cycles of sleep during the week. Lower amounts can provoke insufficient sleep; this can lead to sleep deprivation, affecting the immune system and mental health.
How Much Sleep Do People Need?
According to sleep experts, the amount of sleep needed to stay healthy changes greatly with age. For example, recommended sleep for newborns is between 14 and 17 hours. While this may seem like a lot, it should be noted that newborns sleep frequently for several hours at a time. As the child grows, the recommended resting time gradually decreases.
Adolescents are recommended to sleep between 9 and 11 hours. Adults and the elderly are advised to get only 7 to 9 hours. As mentioned before, sleep is responsible for proper development, maintaining our brain functions as well as our physical health. It becomes evident during extreme growth spurts that good sleep is crucial.
Not getting enough sleep can lead to sleep deprivation. This can have a negative impact on your performance at everyday tasks. Focusing on and learning new information becomes more difficult, and you’re more likely to feel tired and irritable. Achieving the recommended sleep hours will keep you refreshed.
Lack of sleep is quite common in young adults, as it gets less prioritized due to work and leisure. Although many try to “catch up” on sleep during the weekend, it’s simply not enough to prevent negative symptoms of sleep deprivation.
The main characteristic of sleep deprivation is excessive daytime sleepiness. Which later on, if not taken care of, it can lead to other negative side effects interfering with your quality of life.
People who have insufficient sleep tend to get irritated faster than those who sleep the recommended amount of hours. With low energy levels, your motivation drops, affecting your outlook on life.
As the AASM study shows, there’s also a complex cycle in the overall relation between sleep and mental health. A lack of sleep can lead to anxiety or even provoke symptoms of depression, and these conditions can disturb your sleeping pattern even more, which can lead to insomnia.
Sleep-deprived people lack concentration, which can hinder the intake of new information. You also get more distracted due to increased forgetfulness. After a night of poor sleep, your daily tasks might include more errors than usual and your decision-making skills may suffer.
These outcomes may interfere with day to day actions such as driving, working, or learning at school, lowering the quality of your life; this in return might worsen your mental health, putting you in a vicious circle.
As NCBI explains, sleep deprivation also increases your risk of developing a chronic condition. For example, lack of sleep can increase the activity of your sympathetic nervous system, which leads to higher blood pressure.
There are also risks of developing heart conditions, regardless of your age. Insufficient sleep can increase the risk of cardiovascular diseases, one of the common ones being a heart attack.
To prevent sleep deprivation you should practice good sleeping habits. Go to bed and wake up at the same time if possible, make sure you get at least 8 hours of sleep, and avoid drinks that have caffeine in it before bedtime—they will only make it harder for you to fall asleep.
And in case you’re still struggling with falling and staying asleep, you can always give natural sleep aids a try.
This article is for informational purposes and should not replace advice from your doctor or other medical professional.