What is sleep?
Scientifically speaking, sleep is the regular period in every 24 hours when we are normally unconscious and unaware of our surroundings.
Sleep is governed by our body’s internal clock, known as the circadian rhythm and it is this which becomes disrupted when on night shifts or after long flights - giving rise to the experience of being awake at '2 in the morning' when those around you are enjoying a good sleep.
What is sleep for?
Over the years, scientists have been looking into the questions: what is sleep for, and why do we need it?
We now know that a very important role of sleep is to restore our body to full function after the ‘wear and tear’ of the day’s activities. This is especially important for our brain. At night, with normal sleep, tissues are repaired, organs rest or finish cycles such as flushing out toxins and the brain filters and processes the events of the day.
This is perhaps similar to a crew of maintenance staff moving in to sweep, dust, mop and repair your house, mending cracks that have shown up during the day, emptying the rubbish bins, filing the mail delivered and restoring your home to full working order for the next day.
Two types of sleep are described:
- Rapid Eye Movement (REM) sleep.This is what we might call ‘deep sleep’ because it takes longer to wake from REM sleep. Although sleep is deep and muscles are relaxed, the brain is very active and our eyes move quickly from side to side (hence the name). Dreams occur during REM sleep.
- Non-REM sleep. During this type of sleep, our brain is quiet, but our bodies move around the bed more. Hormones are released into the bloodstream and our bodies repair themselves after the wear and tear of the day.
We move from non-REM to REM sleep, and vice versa, approximately once every 90 minutes. During normal sleep we will also have short periods lasting for a minute or so during which we are awake. These take place several times a night and are part of the way our sleep moves through the REM and non-REM phases.
We are not usually aware of these periods of wakefulness. However, we are more likely to remember them if we are worried or anxious, or if there is something happening around you – such as noises outside your bedroom, a partner snoring or going to the toilet.
These short periods of being awake can feel much longer than they really are. For some, this leads to the feeling that one is not sleeping well and a desire to sleep better.
How much sleep do I need?
If asked this question, many of us would answer ‘I need more sleep than what I am getting at the moment’.
It is said that the average person sleeps for seven-and-a-half hours a night. However, averages often conceal large differences and in truth, the amount of sleep a person requires varies considerably.
Age and personality play a fundamental part. Whilst most of us feel we need 7 to 8 hours sleep a night, there are some well-known examples of people who can get by with only 4 hours.
Generally, we need less sleep the older we get. Newborn babies seem to sleep for most of the day and a young child may require about 10 hours. Thereafter, some form of regression appears to take place, as teenagers seem to spend a great deal of time sleeping and experience great difficulty getting out of bed in the morning.
In addition, our normal sleep pattern changes through our adult years. For instance, an older person will sleep very deeply for the first 3 to 4 hours but wake more easily during the second half of the night.