From the importance of sufficient hours of sleep to the various sleep patterns our bodies follow, exploring these stages not only sheds light on our nightly journey but also helps in understanding and addressing sleep disorders that may disrupt this delicate process. In this article, we embark on a journey through the stages of sleep, examining their significance in our overall well-being and the implications for our daily lives.
What happens to your mind and body during sleep?
When we fall asleep, our body and mind undergo a series of changes as we progress through different sleep stages. These stages, which together form a sleep cycle, are characterised by distinct brain wave patterns. Initially, we enter light sleep, where brain waves slow down, and the body begins to relax.
This is followed by deeper sleep stages, where brain waves become even slower, large muscle groups relax significantly, and the body undergoes various physical changes, such as tissue repair and growth. Finally, we reach REM (rapid eye movement) sleep, where brain waves resemble those of wakefulness, and dreaming occurs. Throughout the night, we cycle through these stages multiple times, creating a complex pattern of sleep that is crucial for overall health and well-being.
What are the different stages of sleep?
A lot of people do not realise that we cycle through different stages throughout the night and we are not in one state of sleep. These sleep stages are collectively referred to as sleep architecture, and below we will dive into what is happening during each of these stages.
Stage 1 NREM
As we drift off to sleep we enter stage 1 NREM sleep, otherwise referred to as N1 sleep or ‘light sleep’. During this phase of sleep, our heart and breathing rate will slow, our brain wave activity will slow, our muscles will start to relax and our eyes will do a slow rolling movement whilst your eyelids remain closed. You appear to be asleep; however, you still have some awareness of what is happening around you. It is easy to be awoken from this stage of sleep and often people will not realise they have fallen asleep at all. If left undisturbed, you are generally in this stage for between 1-7 minutes before drifting further into deeper sleep.
In stage 1 NREM sleep, you may experience sudden muscle contractions, or ‘jerks’, or a sensation of falling. These are better known as ‘hypnagogic jerks’ (or hypnic jerks). These are completely normal sensations and whilst they can be unpleasant to experience, they are nothing to be concerned over. It is not yet fully understood why they happen, but they seem to be glitches in the process of falling asleep.
Stage 2 NREM
As we leave stage one, or lighter sleep, everything starts to slow down further. Our breathing rate will become slower and deeper, our heart rate will slow which in turn will lower our blood pressure as well. We start to use less oxygen, so our blood oxygen saturations will also start to dip. Another thing that has to drop is our core body temperature. We must cool down to sleep well and if you’ve ever tried to sleep in a hot bedroom then you can attest to this.
During Stage 2 NREM sleep, or N2, our sensory gating mechanism starts to kick in. This is a system responsible for monitoring everything that happens around us, new sounds, changes in light, smells etc. When your system registers new information, such as a noise, it asks itself “is this a noise I’m expecting to hear?” If it is a known noise (such as your neighbour’s dog that always barks, or the 2 am train going past your house), then it will keep you asleep. However, if it is a new noise you’re not expecting, it will wake you up. This is why we generally sleep poorly the first few nights in a new environment such as a hotel. Every new noise wakes us up.
Stage 2 NREM sleep is also responsible for converting short-term to long-term memories. These aren’t just fact-based memory conversion but skills-based as well, like learning a new physical skill such as an instrument or tying your shoelaces.
Stage 3+4 NREM
Stage 3/4 NREM sleep, N3/4 is also referred to as delta wave or slow wave sleep; as the brain waves start taking on distinctive patterns during this phase. Stage 3/4 NREM sleep is considered to be highly restorative as various functions in the body are increased such as our immune system, tissue repair and growth and cell regeneration. Other various functions important for key bodily processes also start to increase during this deepest stage of sleep.
Our heart rate and breathing rate are generally at their lowest during this stage of sleep and it is difficult to wake someone in this stage. Once awoken, however, they may be slightly confused and it will take a small amount of time for them to become aware of their surroundings again.
REM Sleep
Rapid Eye Movement (REM) sleep is the final sleep stage that makes up your sleep cycle. During this sleep stage, our bodies go into a state of atonia (paralysis), except for our breathing muscles and our eye muscles, the latter of which start producing a rapid back and forth motion that gives this sleeping stage its name. The reason we go into a stage of atonia is so we do not act out our dreams, as REM sleep is when this occurs. It’s during REM sleep that most of your vivid ‘story-like’ dreams occur. You can dream in any sleep stage, but dreams in NREM are generally shorter in duration, more focused on a single emotion and lack the narrative complexity of dreams in REM sleep. During REM sleep, our heart rate and breathing rate will increase and become more variable.
During REM sleep, we see a dramatic increase in brain wave activity, nearing the same levels as when we are awake. One reason for this is that REM sleep produces more activity with our memory consolidation. In NREM sleep, we are converting short-term memories to long-term memories; however, in REM sleep we are taking those new memories and incorporating them into our pre-existing knowledge. This is how we learn to interconnect information and helps us to learn, problem-solve and be creative.
During REM sleep, the emotional centres within our brain also become activated. So not only are we processing our memories, but we are also processing our emotions behind those memories. REM sleep can help take away the ‘sharp edges’ to bad memories, so with time we do not have the same emotional response when we remember difficult times. The expression “time heals all wounds” is not exactly correct, as it should be “time and REM sleep heals all wounds”.
Sleep Stage Distribution
The end of a REM stage concludes one full sleep cycle, which takes approximately 90 minutes. It is common to have a small awakening at the end of a cycle, which the sleeper may not remember in the morning. Then another sleep cycle starts, and a good sleeper will have about 5 cycles in a night. The distribution of NREM sleep and REM sleep changes throughout the course of the night. At the beginning of the night, our first few sleep cycles are made up of predominately NREM sleep. However, as the night progresses, the REM sleep stage becomes longer with the last sleep cycles being made up of predominately REM sleep.
What can affect your sleep cycle?
A variety of factors can influence the delicate harmony of our sleep cycles, often tipping the balance between feeling restful or restlessness. Here are a few common known factors that will impact your sleep cycles:
- Obstructive Sleep Apnoea is a breathing disorder characterised by pauses in your breath, or limitations to your airflow. This reduction in your breathing rate will cause your oxygen levels in your blood to decrease, alerting your brain that you need to wake up. Patients don’t always fully wake up (although some do with a gasping choking sensation), but most go back to stage 1 NREM sleep (light sleep) where they regain muscle control over their airway and can breathe properly again. As they drop down to the deeper stages of NREM sleep or REM sleep this process can repeat. Patients often feel sleepy in the daytime, and may wake with headaches or dry mouths, fall asleep very easily and quickly and wake not feeling rested despite a long sleep.
- Restless Leg Syndrome is similar to sleep apnoea in the sense that the condition wakes them out of deep NREM sleep, but the cause is from muscle twitching instead of a breathing disorder. Patients often complain of an uncontrollable urge to move the legs, pins and needles in their arms or legs, feeling sleepy in the daytime or waking not feeling refreshed after a long sleep.
- Insomnia, whether acute or chronic, is described as taking 30 minutes or more to fall asleep, or waking for 30 minutes or more during the night and this sleep disorder will drastically reduce the amount of total sleep gained in a night. Not only will patients be tired from getting less deep NREM and REM sleep than required, but the regularity of their sleep cycles can be disrupted leading to an even bigger decrease in the quality of sleep cycles.
- Other Sleep Disorders such as narcolepsy, parasomnia, and circadian rhythm disorders further complicate sleep disturbances, requiring specialised intervention for management. If you suspect you may have one of these sleep disorders, then you may need to book in with a sleep specialist who will perform a sleep study to determine the extent of the sleep pattern problem.
- Menopause and its accompanying hot flushes can wreak havoc on sleep architecture, triggering night-time awakenings and disturbances in circadian rhythms. If your sleep is frequently disrupted by hot flushes or other menopause-related symptoms, you might be dealing with menopause insomnia.
- Poor Sleep Hygiene, encompasses habits like irregular sleep schedules, excessive screen time before bed, and consuming stimulating substances like caffeine late in the day, can sabotage the body’s ability to ease into restorative sleep. It’s important to understand what sleep hygiene is and how to maintain healthy habits for optimal rest.
- External Disturbances such as loud noises disrupt sleep continuity, as well as a too-warm sleep environment can make it difficult to move into deep NREM sleep, leading to fragmented and shallow rest.
- Medications, ranging from antidepressants, sedatives and antihistamines, can interfere with sleep architecture, either by directly affecting neurotransmitter balance or inducing side effects like drowsiness or insomnia.
- Alcohol, despite its perceived initial sedative effects, disrupts sleep cycles by fragmenting sleep and reducing the quality of REM sleep. Alcohol is considered one of the worst substances for sleep architecture harmony.
- Underlying Medical Conditions such as chronic pain, gastrointestinal disorders, bladder conditions and neurological diseases can manifest as sleep disturbances, underscoring the intricate interplay between physical health and sleep quality.
- Age As we enter our geriatric years, our ability to produce the deeper stages of NREM sleep become limited. It is also common for the older generation to have difficulty getting the 7-9 hours of sleep needed in one phase and will split their sleep by having a daytime nap.
By navigating the labyrinth of sleep disruptions, addressing these factors through a holistic approach encompassing medical intervention, lifestyle modifications, and behavioural therapies becomes important in restoring the quality of your sleep and making you feel like your sleep actually gives you the restfulness you need.
Ensuring an Uninterrupted Sleep Cycle
Ensuring an uninterrupted sleep cycle involves a holistic approach encompassing various aspects of health and lifestyle. It begins with recognising and addressing underlying sleep conditions by seeking professional help from a qualified sleep consultant. The sleep consultant will do a full assessment on your sleep as well as your health and lifestyle to determine if you have an underlying sleep disorder. They may recommend you to do a sleep test if they deem it medically necessary.
Concurrently, attending to any existing medical issues with your general practitioner or medical specialist is essential, as they can disrupt sleep patterns. Reviewing any medications and the timing of your dosages is also a fundamental part of this, as they may be causing sleeping issues.
Moderating consumption of alcohol, caffeine, and other stimulants in the late hours aids in promoting better sleep quality.
Embracing good sleep hygiene practices, such as maintaining a consistent sleep schedule and creating a conducive bedroom environment, can significantly enhance the ability to achieve uninterrupted rest, fostering overall well-being.
Who Can Help?
It can be really daunting learning all about sleep stages when you are struggling to fall asleep, or know your sleep is not as good as what you want it to be. But don’t be dismayed, help is out there!
Booking an appointment with a sleep consultant who is trained in a variety of sleep disorders can go a long way in pinpointing where your sleeping problems may lie, as they often look at the bigger picture of your health and can recommend the best treatment for your individual sleep complaint. If you’re suffering from insomnia then seeking a sleep consultant who specialises in Cognitive Behavioural Therapy for Insomnia (CBT-I) is your best bet in getting your sleep back to normal.
At TM Insomnia Treatment, we offer online CBT-I consultations so you can seek professional advice from the comfort of your home. They have helped hundreds of patients add hours of sleep back into their nightly routine with their evidence-based and scientific approach to treatment. There are no referrals needed and wait times are currently short, so if you’re interested in getting your sleep back on track, book a 15-minute free one-on-one consultation with Tracey.
Not only is it crucial to understand why sleep is so important and how our health is optimised through each stage of sleep, but it is important to be aware of the various ways our daytime and nighttime habits can impact this delicate cycle. If you feel your sleep could be improved but you’re not really sure where to start, then seeking out the guidance of a trained sleep consultant can be beneficial. The trained sleep consultant will be able to assess all your aspects of health, lifestyle and habits and then guide you on the various ways you can improve your sleep by addressing things you may not have previously considered to be negatively impacting your sleep each night.
Frequently Asked Questions
There is still so much information out there about the wonderful rejuvenating benefits of sleep, so here are some further frequently asked questions that will hopefully satisfy those interested.
What is the best sleep stage?
Each sleep stage is important for different reasons, so there is no one stage of sleep that trumps all others.
Does my smart watch / smart device accurately measure what sleep stage I am in?
The only way to know what stage of sleep you are in for sure, is to measure brain wave activity through electrodes attached to your head and scalp. However, in saying that, the tech behind a lot of these smart devices is improving each year. The way smart devices generally predict what stage of sleep you are in is by measuring your heart rate, your oxygen saturations and the level of movement you are doing. Each sleep stage will vary in these measurements and it uses the data it receives to predict what sleep stage you are in. It does not measure brain wave activity however, so it is possible to fool your devices. The general advice is to use the data it gives you, but if you don’t feel you got as much sleep as what your device is telling you, go by how you feel as opposed to how well your device said you slept.
How much of each stage of sleep should we get?
The breakdown of each sleep stage per sleep cycle varies as we age. However, once you are an adult and you have no sleep disorders that interrupt your quality of sleep, then you should expect to spend approximately 5% of your night in Stage 1 NREM sleep, 50% of your night in Stage 2 NREM sleep, 20-25% of your night in Stages 3 and 4 NREM sleep and 20-25% of your night in REM sleep.
In what stage do we dream?
We actually have dream-like imagery occur in most stages of sleep, however proper dreaming activity will occur during REM sleep. During this time we will enter a state of atonia (paralysis, except for our eye movement and breathing movement) so we do not act out our dreams.
How long does a sleep cycle go for?
A sleep cycle goes for approximately 90 minutes.
How many sleep cycles should we have per night?
An adult should get anywhere between 5-6, 90-minute cycles of sleep each night if they are achieving optimal sleep duration.
How much sleep should we get?
This varies depending on how old we are. For an adult, the majority of us need between 7-9 hours of sleep each night. A small percentage of adults only need 6 hours of sleep and we call them ‘short sleepers’. Alternatively, some need 9+ hours of sleep and they are called ‘long sleepers’. When we are younger, we need more sleep and often break up our sleep into a daytime nap and evening sleep, or in the cases of babies, multiple sleeps throughout a 24-hour period. To read more about how much sleep you need, click HERE (link to other article).
Can you survive on less than 6 hours of sleep per night?
Of course you can survive, but sleep serves a fundamental purpose for our health and well-being. So yes, we can survive, but you may find there are some physical and psychological impacts on the reduced hours of sleep.
What sleep stage is best to wake up from?
It is common to have a small awakening at the end of your REM cycle, so if your sleep was timed perfectly, you would be waking after a period of REM sleep in the morning. Waking in the middle of a deep sleep or in the middle of your REM cycle can be a little difficult as it may take you a longer period of time to adjust to the reality of waking and clear away any confusion. If you’ve woken up mid-dream and it has taken you a little while to realise the dream was in fact, just a dream, then you can relate to this.
Is it normal to wake up during the night?
Absolutely yes! In fact, it is quite normal to have a short awakening at the end of your REM cycle. However, it is quite common to not remember these awakenings, since they are often only a couple of seconds and don’t necessarily involve the sleeper to open their eyes. Often they may just readjust their sleeping position and restart the sleep stage cycle. What is not normal however, is having difficulty going back to sleep or if you start to associate the awakening with negative significance. If you feel like you’re having too many awakenings (even if they’re very short) it could be a sign of an underlying sleep disorder and it is important to seek advice from a medical professional trained in sleep medicine. If you feel like your awakenings are longer than necessary and you have difficulties falling back asleep, then you should also reach out to a medical professional trained in sleep.
Do all animals have sleep stages like us?
No, there is a lot of variation in sleep cycles in the animal kingdom. Since your body is in a state of atonia during REM sleep (your muscles are paralysed) this can pose a problem for some creatures who need to constantly move to survive (think of swimming fish) or to stay in a tree for safety. For these reasons, many animals only have small bursts of REM sleep for survival, or half of their brain will enter REM sleep whilst the other half continues normal functioning. Some animals will also change their sleeping cycles at different points in their life when they need to be
