Summary
- Sleep needs vary.
- Sleep is an active state.
- Deep sleep happens first.
- Sleep changes in cycles.
- A body clock affects our tiredness.
- Falling asleep can be hard.
- Lack of sleep can bring you down.
- Genetics and sleep.
- Why do we sleep?
Sleep need varies
Different people need different amounts of sleep. Eight and a quarter hours is the average for adults. Some people can cope very well with much less and some need much more every night.
Sleep is an active state
We used to think that everything shuts down when we sleep. But over the last 60 years scientists have discovered that our brains are very active while we sleep. In fact, some parts of the brain use more oxygen and glucose while asleep than when awake.
Deep sleep happens first
The first three hours of sleep have the deepest stages of sleep (Slow Wave Sleep). Later on in the night we have more of the sleep stage with vivid dreams (Rapid Eye Movement Sleep, REM sleep).
Sleep changes in cycles
Sleep changes across the night in cycles of about 90 minutes. There is REM (dreaming) sleep in every cycle, even if only for a short time. We also have very brief arousals many times across the night. We are not aware of most of these arousals and we forget most dreams.
A body clock affects our tiredness
The timing of our need for sleep is based on two things. The first is how long we have been awake. The second is our body clock. If we stay awake all night we will feel more tired at 4am than at 10am. Scientists call the time between 3am and 5am the ‘dead zone’. It’s when our body clock makes us ‘dead’ tired.
Falling asleep can be hard
You cannot make yourself fall asleep – just like you can’t digest your food faster. Sleep onset is not something we can control. We can only create the right conditions for sleep – both in our minds and in our environment.
Lack of sleep can bring you down
Some people cope with a lack of sleep much better than others. But everyone who is very sleepy loses concentration easily and experiences mood changes. The usual mood changes are feeling more depressed and irritable.
Genetics and sleep
We now believe that many aspects of sleep are genetically controlled. Recent breakthroughs may have identified the gene that makes some people cope more easily with a lack of sleep.
Why do we sleep?
Scientists don’t yet understand exactly why we need sleep so badly. They believe it restores us physically and helps us organise things in our brain. We do know, however, that we can’t live well without it.