The Sleep Cycle


Sleep is something that influences the way our body functions on a day to day basis. It helps us to rest, recharge, heal and recover. The amount of sleep one needs differs from person to person. Sleep needs also change from birth to old age. Being sleep deprived can impact us negatively in multiple ways such as:

  • Cognitive loss- memory and concentration
  • Severe moodiness
  • Hyperactivity in children
  • Health problems including obesity, heart disease, hypertension and diabetes
  • Risk of injury due to accidents

Have you ever experienced sleeping for fewer hours at times and waking up feeling more rested than when we sleep for 8 hours or more? It is quite possible because it does not really depend on the number of hours that we sleep as much as the number of full cycles of sleep we experience and in which stage of sleep we wake up. Understanding the sleep cycle and what our body is upto when we are asleep may help us to optimise our sleep schedule and help us wake up feeling rested and refreshed. 

The Sleep Cycle

Our nightly sleep is made up of many sleep cycles and each cycle consists of different types and stages of sleep. Falling into deep sleep is a continuous process and there is no sharp demarcation between the various sleep stages. 

There are 2 main types of sleep. 

  1. Non Rapid Eye Movement Sleep (NREM) which consists of 3 phases NREM 1, NREM2 & NREM3 and 
  2. Rapid Eye Movement Sleep (REM)

Sleep is divided into 4 stages and each stage has different features. They are essential for the body’s physiological and psychological health. If any stage of sleep is missed, its functions will not be fulfilled and we may feel tired and not sufficiently recovered even after an adequate period of sleep at night.

The 4 Stages of Sleep

1. NREM Stage-1: It is usually the first few minutes of sleep where the transition between being awake and falling asleep happens. You are aware of your surroundings at this stage and can easily be aroused back to wakefulness. Dreaming is rare at this stage although a hypnotic jerk may be experienced sometimes when falling off to sleep and is accompanied by the sensation of falling down. Only 5% of our total sleep time is spent in this stage of sleep.

2. NREM Stage-2: It is the stage between light and deep sleep. The metabolic activity of the body reduces at this stage. Heart beat slows, blood pressure and body temperature reduce and breathing slows down. The awareness of the surroundings stops and eye sleep stagesmovements stop. This is the body’s way of  preparing for deep sleep. A person can be easily woken up in the initial phase of this stage. We spend most of the time (almost half 45%) every night in this stage. 

3. NREM Stage-3: It is also known as ‘slow wave sleep’ or ‘delta sleep’. This is the deepest level of sleep. We are unaware and cut off completely from the outside world. It is difficult to wake a person who is in this stage of sleep. Heart beat, blood pressure, breathing rate, nerve activity and all metabolic functions are at their lowest levels in this stage of sleep. We spend 25% of our total sleeping period, in this stage of sleep. NREM Stages 2 and 3 are important for memory consolidation and information processing.

4. REM Sleep: The first REM sleep episode generally occurs after 90-110 minutes of sleep, cycling about every 90 minutes thereafter.  REM sleep periods tend to be longer later in the night. Heart rate and breathing rate increase and become irregular in this stage. Dreaming is most common in this stage. Many of us will remember dreams from the REM stage.  The body creates chemicals that render us temporarily paralysed so that we do not act out our dreams. In this stage, the brain is extremely active and our eyes, although closed, dart back and forth as if we were awake. This stage is also important for memory consolidation and for our ability to learn complex tasks.

During the course of an eight hour sleep period, a healthy sleeper should cycle through the various sleep stages. It may consist of 4 to 5 sleep cycles that go through the above 4 stages. The first sleep cycle is typically around 90 minutes. However, the length of the cycle varies from individual to individual.

Each cycle follows the sequence of NREM Stage 1 & Stage 2, followed by a longer period of NREM Stage 3. It then goes back from NREM Stage 3 to NREM Stage 2 and Stage 1, followed by a brief period in REM sleep. Then a new cycle begins. NREM Stage 3 is usually longer in the first half of the night. Waking during deep sleep (NREM Stage3) or REM Stage can leave you feeling drowsy and sluggish. If you sleep too long and miss the light sleep at the end, chances are you will wake up feeling sluggish, fatigued or drowsy. A power nap during the day is great because you won’t experience any sluggish or drowsy feeling after waking. This is because you do not enter into any deep sleep during this brief time. It is best to wake up in a light sleep stage (NREM 1 & 2).

Sleep patterns can be affected by many factors, including age, the amount of recent sleep or wakefulness, the time of the day or night relative to an individual’s internal clock, other behaviours prior to sleep such as exercise, stress, environmental conditions such as temperature and light and various chemicals.

Guidelines for Better Sleep

  • A good comfortable mattress to maintain a good sleeping posture.
  • Quiet environment away from noise. Use earplugs if necessary.
  • Try to maintain a cool temperature in the bedroom. Not too hot or too cold.
  • Avoid exposure to bright lights as they interfere with the melatonin production which helps induce sleep. Use an eye mask if necessary.
  • Avoid use of electronic devices prior to bedtime.
  • Maintain regular sleeping hours and avoid taking long naps during the day.
  • If a person is drowsy or tired during the day, a 15 to 30 minute power nap can be sleeping1taken.
  • Avoid exercise prior to bedtime. Maintain a 3 to 4 hours gap between evening workout and bedtime.
  • A relaxing or quiet activity like listening to soothing music, deep breathing, meditation, etc.  may help to calm the mind and prepare for sleep.
  • A lukewarm bath can help relax the body and muscles preparing for sleep. Avoid hot bath as it increases body temperature which may make it difficult to fall asleep.
  • Avoid stimulants such as caffeine close to bedtime. Caffeine reduces the natural melatonin production.
  • Avoid a heavy meal close to bedtime as it can increase the tendency of digestive discomfort or acid reflux.
  • Ensure you have had sufficient water intake throughout the day. Preferably  reduce fluid intake 1-2 hours before bedtime or from evening onwards, depending upon the person’s tendency for frequent urination.
  • Consuming food rich in tryptophan such as fish, eggs, nuts, etc can help promote sleep and drowsiness.
  • Avoid sugary, oily, fermented and processed food in dinner and close to bedtime as they can disrupt sleep.

“Discover the great ideas that lie inside you by discovering the power of sleep.”

-Arianna Huffington


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