Sleep: A beginner’s guide
Sleep is important to allow the body to rest and get ready for the next day, and to help recover from illnesses.
A good night's sleep also helps with mental health, stress and problem solving.
What happens during sleep?
Sleep is prompted by natural cycles of activity in the brain and consists of two basic states: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep, which consists of stages 1 to 4.
During sleep, the body alternates between non-REM and REM sleep. Typically, people begin the sleep cycle with a period of non-REM sleep followed by a very short period of REM sleep. Dreams generally occur in the REM stage of sleep.
What is non-REM sleep?
The period of NREM sleep is made up of stages 1 to 4. Each stage can last from five to 15 minutes. A completed cycle of sleep consists of a progression from stages 1 to 4 before REM sleep is attained, then the cycle starts over again.
- Stage 1: Polysomnography (sleep readings) shows a reduction in activity between wakefulness and stage 1 sleep. The eyes are closed during stage 1 sleep. One can be awakened without difficulty. However, if aroused from this stage of sleep, people may feel as if they have not slept. Stage 1 may last for five to 10 minutes. Many people may experience the feeling of falling during this stage of sleep, which may cause a sudden muscle contraction (called hypnic myoclonia).
- Stage 2: This is a period of light sleep during which polysomnographic readings show intermittent peaks and valleys, or positive and negative waves. These waves indicate spontaneous periods of muscle tone mixed with periods of muscle relaxation. The heart rate slows and the body temperature decreases. At this point, the body prepares to enter deep sleep.
- Stages 3 and 4: These are deep sleep stages, with stage 4 being more intense than stage 3. These stages are known as slow-wave, or delta, sleep. If aroused from sleep during these stages, one may feel disoriented for a few minutes.
During the deep stages of NREM sleep, the body repairs and regenerates tissues, builds bone and muscle, and appears to strengthen the immune system. As you get older, you sleep more lightly and get less deep sleep. Ageing is also associated with shorter time spans of sleep, although studies show the amount of sleep needed doesn't appear to diminish with age.