This is a common question many people ask me.

Before I answer this question let me briefly describe what sleep is.

Sleep is

  • a highly complex and active process of dynamic restoration, rejuvenation, recuperation,  and reconsolidation, all of which are essential for health and wellbeing.
  • a fundamental and highly complex biological phenomenon. Neurotransmitters in the brain control our sleeping patterns in interaction with neurons.

Neurotransmitters such as serotonin and norepinephrine keep some parts of the brain active while we are awake. Other neurons at the base of the brain begin to signal when we fall asleep, “switching off” the signals that keep us awake. Chemicals are central to sleep, particularly adenosine, which is produced by our cells, accumulates in our blood and travels to the brain while we are awake and causes what we experience as sleepiness. This chemical gradually breaks down while we sleep and allows us to wake. Yes, sleep has complex biology.

The stages of sleep

Our nightly sleep is composed of a number of sleep cycles, each of which is made up of different stages. There are two main types of sleep – non-REM and REM sleep – and the differences between them are almost as profound as the differences between sleep and wakefulness. Scientists today use a variety of technologies to understand the diverse aspects of sleep by measuring the electrical activity of the brain, the muscles, and movement of the eye.

It is now understood that we pass through five stages of sleep as we fall from wakefulness, with REM (rapid eye movement) sleep the final of these stages. These stages progress in cycles, moving through stage 1 to REM sleep and then back to stage 1. The progress of each cycle lasts around 90 minutes in adults and 30–40 minutes in children. During the first stage, which lasts approximately 15 minutes, we actually move back and forth between wakefulness and sleep. Brain waves during this stage give way to alpha waves. In the second stage, we enter what can be termed the first “real” sleep. Here theta waves begin to appear as we enter a phase which comprises 50% of our sleep time. During this stage, the body prepares to enter deep sleep. Both stage one and two are relatively light stages of sleep. The third and fourth stages of sleep are termed “slow wave sleep” and we spend approximately 20% of our total sleeping time in these stages. Here we experience delta waves and a form of deep sleep from which it is very hard to wake. REM is the last stage of the sleep cycle. As rapid eye movement begins, our skeletal muscles are virtually paralyzed. The brain wave pattern shows a blend of alpha and beta waves. During this stage, our breathing becomes more rapid, irregular and shallow, and our heart rate rises along with blood pressure. It is at this stage that males develop penile erections. REM is the stage during which we dream, often in a bizarre and illogical form. The first period of REM usually has a duration of 10 minutes. Each subsequent REM stage increases in duration, with the final one lasting up to an hour.

Why we sleep?

It is still not understood why we evolved the need to sleep. What is clear is that sleep, as with breathing, is a fundamental human requirement and not somehow an optional add-on during life. Studies into animals show that sleep is a prerequisite for survival. Rats, for example, typically live for 2 to 3 years. Those deprived of REM sleep survive only about 5 weeks on average and rats deprived of all sleep stages live only 11–32 days.

Sleep-deprived rats develop a number of ailments: abnormally low body temperature and sores on their tail and paws, to name two. Some studies suggest that sleep deprivation affects the immune system in detrimental ways. The sores developed by the sleep-deprived rats seem to be evidence of an immune system imbalance caused by a lack of sleep. Sustained sleep deprivation can lead to mental disturbance, anxiety, tiredness, fatigue and even death if prolonged. There are reports of cases outside scientific studies where people have died after periods of no sleep at all. In such cases, people experience symptoms of hallucinations, weight loss and finally dementia before their death. Sleep is so important to well-being that scientists argue that animals can survive for three times as long without food as without sleep.

How much sleep do we need?

It is well known that people need approximately 8 hours of sleep every night, but to be precise we need around 7.5 hours. As each sleep cycle has a duration of about 90 minutes, and we need 5 such cycles, the total for recommended sleep is 7.5 hours. Sleeping well depends not only on the number of hours but on the quality and consistency of sleep. Intuitively, we experience this. One can spend 10 hours in bed and still feel tired in the morning.

Sleep calculator

To calculate in a meaningful way the sleep we require, and to know when we should be going to bed, we need to work backward and define the time at which we need to get up. For example, if we need to rise at 7 am, we need to, firstly, count back 7.5 hours, which brings us to 11.30 pm. Yet getting to sleep is a process and requires sleep onset latency, a period of time required to fall asleep after lights have been turned off, which lays the foundation for a solid night’s sleep. This period should be about 10–20 minutes. Allowing, therefore, for 20 minutes of sleep latency, 11.10 pm can be defined as the time to be getting into bed to get enough hours of quality sleep, assuming a reasonable quality of sleep ensues. Interestingly, if you find yourself asleep as soon as you hit the pillow, this may be an indicator of sleep deprivation. If the onset of sleep takes longer than 20 minutes, this may be a symptom of insomnia.


Dr. Andrew Arnold has known the author for several years and endorses her as an expert in the field of sleep.

Find out more about sleep and how you can get better quality sleep in my book: FIX MY SLEEP book, By Sveti Williams – Sleep Coach


Fix my sleep book:





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Category: Sleep

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