Stages of Sleep and Sleep Cycles

You’ve had a long day, and all you want to do is retreat to the quiet sanctuary of your bed. But, have you ever wondered what goes on in your head while you’re resting? Sleep is an important part of your daily routine but it’s often taken for granted.

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    We spend about one-third of our lives  sleeping; or at least attempting to do so. Doctors stress that good sleep, is as essential to us as water or food. So, what is the biological purpose of sleep and why is it so important?  Simply put, it rejuvenates both your body and mind on a daily basis. Sleep deprivation can negatively affect performance at work or school. It can  also adversely change your overall mood, disrupting relations with family and friends. We’ll delve into the various stages of sleep and how they impact how productive your sleep is.

    Sleep Cycle Stages

    The actual amount of sleep one needs varies throughout your life. For adults, 8 hours is prescribed by experts. During this period,  your body goes through about four to five cycles of sleep during that period before waking up. These cycles can last up to 90 minutes. Each are linked to neuron activity and particular brain functions. The first four stages involve the NREM (non-rapid eye movement) sleep, whereas, the REM (rapid eye movement) sleep occurs in the fifth stage.

    Sleep Stage I (NREM)

    This is the stage when you start to get drowsy. This is a transition period that can last anything from 15 seconds to 15 minutes. The breathing gradually gets irregular and shallow and the eye movements also slow down, but you can be roused easily because you respond to disturbances easily. If you have ever experienced a falling sensation during sleep, this is the stage of sleep you were in.

    Sudden twitches are common in this stage. You may also experience a sudden dream onset. This is the stage where you have heard people say, “Oh, I wasn’t sleeping!” or “Oh, I was just half asleep.” Most people, when woken up during this stage will not even acknowledge they were asleep and yet many more experience sudden muscle contractions.

    Sleep Stage II (NREM)

    During this stage, the muscle contractions decrease rapidly and come to a halt, and the level of consciousness decreases considerably. The body is entering light sleep and the blood pressure drops and heart rate slows down. The body is not aware of  its surrounding environment and Brain activity slows down. Typically, half of all sleep time is spent in this stage.

    Sleep Stage III (NREM)

    This stage is known as the delta stage, or simply deep sleep. Its responsible for your body  waking up refreshed in the morning. During this stage, the body repairs and heals itself. We becomes less and less responsive to outside stimuli and become difficult to wake up. This is also the stage  associated with sleepwalking, wetting the bed or talking in your sleep. Your brain waves become slower as the actual onset of sleep begins.

    Sleep Stage IV (NREM)

    This period is a continuation of stage 3 and has the same symptoms. This is also a regenerative period and the body repairs tissues and develops muscle. If you were to wake up during this period, you would be disoriented and it would take you a while to realize where you are. This is stage 4 of sleep.

    Stage V (REM Sleep)

    During this period, the brain s very active. This is what makes this stage, the rapid eye movement or stage 5, very different from the others. The first such period lasts approximately 10 minutes but keeps doubling up as the night progresses. Adults spend about 20% of the total sleep time in this stage, while infants spend nearly 50%. The brain activity in this stage is similar to that of a wakeful state. The eyes dart back and forth behind the eyelids and the brain is buzzing with activity, dreaming and thinking.

    The blood pressure and heart rate are close to that of a wakeful state and you are unable to move your legs (they are paralyzed, as a matter of fact), stopping you from acting out your dreams. You are likely to remember dreams that occur in this stage quite vividly.

    When the sleep cycle nears its end, you will start waking up, the body’s temperature will go up and the heart rate goes back to the daytime levels. Most people will wake up after or during the REM cycle.

    Sleep Stage Cycles

    Let’s break down a typical day in 6 stages and summarize what we have learned so far:

    The State of Wakefulness

    This stage is not really a stage, but the period when you are wide awake. Your eyes would be open at all times (barring the time when you blink, which amounts to over 20,000 times a day!). In this stage, you would do what any healthy person would do — you would be aware of your surroundings, you would hold long conversations, and your responses to most things would be normal. This state lasts from 14 to 18 hours a day, depending on a lot of factors such as what you do for a living.

    The State of Drowsiness

    This would be the time when you start feeling rather dozy. This is more like a transition between wakefulness and sleep. This stage is so light that if woken up, you won’t realize you were asleep. This stage lasts from anywhere between 15 seconds to 20 minutes. A lot of drivers who have had a lack of sleep experience this, and sometimes, end up in accidents.

    The State of Light to Very Light Sleep

    During this stage, your muscles are relaxed and your consciousness levels drop. The eye movements stop, and the body temperature goes down. This stage generally lasts from anything between 10-25 minutes.

    The States of Deep and Very Deep Sleep

    These are the stages 3 and 4 since they are not very dissimilar. You go into deep sleep and it becomes difficult for someone if they are trying to wake you up. The brain waves work at a much slower rate. This stage lasts for about 40-60 minutes.

    The REM State

    Similar to the wakeful state, the brain is on fire at this stage. You will dream and remember most of it, the body stops moving and the brain is working on preserving memory.  The REM cycle occurs 1.5 hours after you fall asleep, and lasts up to 1 hour.

    What Exactly Is a Sleep Cycle?

    The fact that sleep goes in cycles has been known since the mid-1900s, it alludes to the time-frame it takes an individual to go through the periods of rest as we explained before. A sleep cycle is what it sounds like, a cycle. If you were to fall asleep, you would not directly switch to REM sleep and skip all the other 4 cycles.

    It goes something like this — from light sleep to deep sleep, then it reverses and goes from deep sleep to light sleep, and just before that, switching to REM sleep. Think of the REM sleep as a timestamp, because every time after REM, a new cycle begins. As the night deepens, the sleeper spends more time in REM, and less and less time in deep sleep. During a night, a person sleeping can go through as many as 4-5 such cycles and each cycle can last up to about 2 hours.

    How Is Deep Sleep Different Than REM?

    Glad you asked, because people often confuse the two. They are as different from each other just as light sleep is different from deep sleep. REM and deep sleep are two different sleep cycles and have their own characteristics. Deep sleep occurs in stages 3 and 4 of the cycle, whereas REM is considered the 5th stage (though in some texts, you may find it being referred to as the 4th stage. This is because stages 3 and 4 or the sleep cycle are not very different).

    To compare the two and for you to understand the concept better, we will break each into 4 categories, namely time, length, brain and body.

    REM Sleep

    While in this stage, the eyes move rapidly from side to side behind the eyelids. You are likely to remember any dreams that you experience during this stage.


    The body remains largely inactive during this stage, but your heartbeat resembles that of when you are in a wakeful state, and so does the blood pressure.


    Your mind is a flurry of activity during REM sleep. As we mentioned earlier, you are likely to experience the most vivid dreams and remember them too. Also, bedwetting and sleepwalking happen only during this stage. REM works towards restoring your brain and is essential for your memory as well as learning.

    Time It Starts

    A person will experience REM sleep approximately 1.5 hours after falling asleep.

    Length of Sleep

    There are up to 5 rounds of REM sleep every night, and the first one can be as short as 10 minutes. The length of the REM sleep keeps increasing throughout the night, and the last round can last up to 1 hour.

    Deep Sleep

    Sometimes also known as the N3 sleep or slow sleep wave, the body undergoes repair under this stage, and the brain slows down.


    During this stage, the body undergoes a lot of changes — the muscles in the body become relaxed and the heartbeat regularizes during this stage. You are likely to sleep through distractions such as loud noises. Also, the body builds muscle tissue and repairs cells in this stage.


    You are unlikely to wake up during this stage, but if you do, you will be very disoriented. You will also almost never dream during this stage.

    Time It Starts

    After falling asleep, the body will enter deep sleep within 45 minutes or an hour.

    Length of Sleep

    Deep sleep consists of 20-25% of your overall sleep and can last as long as 2 hours. And remember, different persons have different sleep needs.

    More about REM Sleep

    Think of REM sleep as one complete half of your entire sleeping period; the first half being the other four stages. An ordinary person experiences up to 5 cycles of REM during a night’s sleep. REM sleep occurs about 90 minutes after you fall asleep, and the first cycle lasts for about 10 minutes.  But this number increases consecutively, and can eventually be up to 1 hour.

    During REM sleep, the eyes move continuously side-to-side and the brain is in an overdrive. Males will wake up with erections (because the testosterone levels are high), and the blood pressure rises.

    A person is likely to wake up during the end of the REM sleep and the heartbeat goes back to the daytime levels.

    Dreams and REM Sleep

    You are likely to experience the most likely dreams during the REM stage, and it is because your brain is extremely active at that time. That is the reason that if you are woken up during the REM cycle, you can possibly describe the dream in vivid detail.  As we mentioned before, the muscles are partially paralyzed during this cycle, and it is widely believed that this is to prevent us from acting out our dreams and injuring ourselves.


    Understanding the stages of sleep can help you better appreciate their importance. It takes approximately 90 minutes to complete a full sleep cycle. Each stage plays a unique and significant role in the process. Today’s active lifestyles often make getting the rest you need next to impossible. Interrupted, non productive sleep will not allow your body to properly recuperate. For better health, start today by making and keeping a consistent sleep schedule. We recommend taking an active interest in how productive your sleep actually is. Consider a  Fitbit or sleep tracker device to help bring your progress into focus. They monitor your light, deep and REM sleep and offer guidance in attaining your goal. Remember, better sleep means better health!