The average person sleeps eight hours a night, which amounts to 3 000 hours a year and means we basically sleep for a third of our lifespan. Incredible when you think about it! But the average person is not aware of what happens during that third of his or her life. Studying sleep is fascinating and offers great insight into why a good night’s sleep is important.
Basics of sleep
Sleep can be divided into two main types:
- Non-rapid eye movement sleep, or NREM, also known as quiet sleep
- Rapid eye movement sleep, or REM, also known as active or paradoxical sleep.
The sleep cycle is divided into five stages of sleep, with the cycle repeating itself four or five times during a sleep period, roughly every 90 minutes.
The first four stages happen during NREM, while REM constitutes the fifth and last stage of sleep.
Five stages of sleep
Stage 1: falling asleep
This is a light stage of sleep, the period between wakefulness and sleep when the muscles start to relax. This stage takes up about 5 to 10% of a sleep cycle. It is easy to wake someone during this stage of sleep.
Stage 2: light sleep
During stage 2 brain waves start slowing down, eye movement stops, body temperature decreases, heart rate slows down and we lose normal consciousness. This takes up about 40 to 50% or up to 20 minutes in the sleep cycle.
Stage 3: middle-deep sleep
A transitional period between light and deep sleep, this stage see the emergence of deep, slow brain waves known as delta waves. It lasts between 10 and 15 minutes in a sleep cycle.
Stage 4: deep sleep
The deepest of the sleep stages with slow delta brain waves, this lasts for about 30 minutes in a sleep cycle. Body movements appear at the end of this stage and this would also be the most likely time when sleepwalking, night terrors or bed-wetting will appear.
Stage 5: REM sleep
Stage 5 is REM sleep, when most dreaming occurs. The heart and breathing rate speed up and the eyeballs move rapidly, while blood pressure rises and around a 20% rise in brain activity occurs. In contrast the muscles are virtually paralysed. REM sleep accounts for between 20 to 25% of a sleep cycle, but with children it takes up a larger proportion of the sleep cycle.