Sleep is a surprisingly complex and dynamic process. It is a particular kind of rest that is important for our physical and mental health. Sleep is as essential to good health as oxygen, food, and water. Even though we might think of it is as a passive, dormant part of daily life, it is actually a time when parts of the brain are more active than during wakefulness! We cannot live without sleep, it assists with growth, repair, memory, mood and pretty much every type of tissue and system in the body. Research shows that a chronic lack of sleep, or consistently poor sleep quality, increases the risk of many common disorders.
For more information on the basics of sleep, visit Better Health.
When we are functioning well, sleep happens automatically, and we don’t need to give it much thought. Our bodies are attuned to our environments and activity and will automatically give us the type and amount of sleep that we need.
There are four typical stages of sleep. Stage 1 is light sleep as your body is winding down. Stage 2 is where we spend most of our time when asleep, whilst stages 3 and 4 are deep sleep. Finally, there is rapid eye movement (REM) sleep which is the stage where our most vivid dreaming occurs. Interestingly, our bodies go into a paralysis-like state during REM sleep so that we stay safe and don’t act our dreams! One complete sleep cycle (i.e., Stage 1 through to REM) takes about 90 minutes. In the image below, we can see five sleep cycles across the period of sleep. The pattern is rather like a rollercoaster as we cycle through the sleep stages.
We are most prone to waking up when we transition from one sleep cycle to the next. In the image below we can see two instances of being awake, both at the end of two of the sleep cycles. This is entirely normal and healthy. It is thought that humans have evolved to wake up a few times during sleep, so that we could check our surroundings to ensure our safety. Perhaps we can be thankful for our ability to wake up, as without it, humans may not have adapted and survived this long!
Interestingly we obtain nearly all our deep sleep in the first four hours of the night (see image below). So, even if you only got to sleep four hours on a particular night, you might have been able to get the same amount of deep sleep as someone who had an eight-hour sleep.