What happens when we close our eyes and begin to drift off to sleep?
Over the course of the night, our sleep is made up of several rounds of the sleep cycle, which is composed of 4 individual stages.
If we have a full night of uninterrupted sleep, the stages progress as follows:
Sleep cycles occur regularly, roughly every 90 minutes, so on average we experience around 4-6 sleep cycles in a 7–9-hour sleep period.
After the 4th stage / REM/dream sleep phase, the body returns to stage 2 / light sleep and the cycle repeats.
Time spent in each stage changes throughout the night.
Stage 1 is essentially the “drifting off” stage, and it normally lasts just 1-5 minutes. This is the transitional state of consciousness between wakefulness and sleep –known as hypnagogia.
In this stage, the mind and body begin to ‘slow down,’ causing us to feel relaxed and drowsy.
When people are wakened during the initial stages of falling asleep, they often report having experienced flashes of dream fragments. These fragments of dream-like experiences tend to occur on the cusp of sleep, as the unconscious, imaginative mind takes over from conscious thinking (or worrying).
Usually, these fragments are visual, auditory, or tactile. However, they can also involve our other senses or feelings of movement. E.g. sensations of flying or falling.
During stage 1 sleep a high level of both alpha brainwaves (associated with deep relaxation) and theta waves (associated with drowsiness) are produced. The individual experiences a “half-asleep” feeling while making the transition from wakefulness towards sleep.
Stage 2 sleep can last for 10-25 minutes during the first sleep cycle and each phase of light sleep can become longer during the night. Altogether we typically spend about half our sleep time in this light sleep phase.
In this light sleep phase, the body enters a more quiet state, including:
In this stage, the brain produces sudden spikes in brain waves known as sleep spindles (because of their spindly appearance on EEG charts). These spikes in brain activity appear to have a role in long term memory consolidation and sensory processing, making this an important stage as we age.
This stage – also called slow wave sleep or delta sleep – is characterised by the production of slow, delta brainwaves. During this period of deep sleep any noises or disturbance may fail to wake the sleeping person.
Deep sleep phases last longer during the 1st half of the night and they reduce in length during the latter part of the night’s sleep. Dreaming (REM sleep phases) follow the reverse pattern i.e. most dreaming normally takes place in the later part of the night’s sleep.
Getting enough deep /slow wave sleep allows us to feel refreshed the next day.
Deep, slow wave sleep is vital for our mental and physical health.
Dream (REM) sleep is so named because the eyes are darting about rapidly under closed lids.
Normally we don’t enter the dream/REM sleep stage until about 90 minutes into the sleep cycle. As the night goes on, the dream stages get longer, especially in the second half of the night. While the first period of dreaming may last only a few minutes, later stages can last for around an hour. In total, dream/REM sleep makes up around 20-25% (1 ½ – 2 hours) of sleep each night in adults.
It’s not just how much or how little sleep we get, but the quality and composition of that sleep that is important for health.
The right quality of sleep (around 20%-25% dream/REM sleep to 75-80% non-REM sleep) determines mood, motivation and emotional stability during the day. Sleep is fundamental to our mental and physical health.
Most teenagers need 8-10 hours of sleep per night – a few hours more than the average adult. Teenagers’ body clocks naturally shift to make them feel tired later in the evening, but early school starts do not enable them to sleep in the mornings. Consequently, many teens are not getting as much sleep as they need.
Chronic sleep deprivation can have dramatic effects on a teenager’s mental wellbeing and academic performance at school.
Research shows that people who worry excessively dream much more than those who don’t, disrupting the balance between recuperative slow-wave sleep and energy-burning dream sleep. Deep restorative sleep time is reduced while dream (REM) sleep time starts earlier, for longer periods and dreams are more intense.
This is because people suffering from depression spend so much time worrying and imagining, so they have much higher amounts of unexpressed emotional arousal to discharge. With so much energy spent on all the excessive dreaming this requires, they then wake up exhausted, lacking in motivation, with limited ability to concentrate.
We have known since the 1950s, for example, that people with depression, who worry continually, dream up to three times as much as normal and wake up feeling exhausted even after many hours sleep. (This happens whether they recall those dreams or not). This is because they have more unresolved emotional arousals. Dreaming is our natural way to deactivate the excessive undischarged emotional arousal that results from excessive negative rumination.
It’s therefore important not just to get 7-9 hours of sleep per night, but to ensure it’s the right balance/quality of sleep that allows your body to benefit from each of these four stages.