Sleep is not a static state. It turns out, one does not simply “sleep”. It is an ongoing process. Your body and brain maintain the balance needed to rest, repair and recover.
Sleep is also rather complex. Beyond us there are many things that can go wrong – pets jumping on and off the bed, bed partner moving about, children calling out at night, stress affecting our physical rest and dreams. Sleep turns our senses right down and it also diminishes our memory so we may not even be aware of these disruptions.
Sleep disorders can disrupt your sleep with sudden movements that jolt your brain into wakeful function, or breathing issues that keep waking you and preventing deep sleep.
As sleep is a process, it is not simply an on/off switch that your body will flick once you are just the right amount of relaxed. While you are still awake, your body and mind will already be driving you towards bed before you are even aware of it. Once you are in bed ready to sleep your body and mind will progressively enter sleep and deeper states of it.
This process has to repeat itself if you are woken up. And it is the same process that sends you deeper and deeper asleep to the all-important deep stages of sleep, known as slow-wave sleep (your brain slows right down), and rapid eye movement sleep (underneath your eyelids, your eyes move, and you have the most vivid dreams at this time of night).
Sleep measures
Sleep measurement presents some wicked problems to the scientist. You cannot see or feel anyone else’s sleep. You cannot measure their sleep from within. All you can do is describe it from external observation and measure, and in doing so, you might change sleep itself by measuring it. The more sensors or attention you give to the act of measurement, the more likely you are to affect sleep.
Polysomnography
Literally means many graphs of sleep. That is what it looks like on paper or a computer. Polysomnography consists of a few dozen sensors on the head and body to measure brain waves, eye movements, muscle activity, position, breathing, oxygenation and airflow. The test itself can affect the sleep it is measuring. Despite this, most people do manage to get some sleep, albeit of a worse quality. People with insomnia, sensory sensitivities and children are more likely to experience discomfort.
Actigraphy
These are a wristwatch-like medical device that measures sleep by using an accelerometer to measure the movement, with movement indicating wake and stillness indicating sleep. Nowadays, you can buy consumer versions of these in fitness trackers and smartwatches.
Novel sensors
Sleep technologies are a rapidly changing field. There are innovative ways to do what polysomnography or actigraphy might do and there are new technologies that try to completely do away with them.
Bed pressure sensors use a sensor in the linen, mattress, frame or legs to detect movement, and similarly to actigraphy, use this to infer sleep and wake.
Non-contact physiology sensors such as radiofrequency and infrared combine sound or video with machine learning to identify body position, movement and whether someone is asleep or awake.
Circadian, light and endocrine
Light is the strongest driver of your sleep-wake rhythm. Light itself can be measured but that does not tell us what your body is doing with light exposure. By taking samples of saliva or blood we can count the hormone levels that would affect how sleep you feel and when you feel it.
Questionnaires
There is a wealth of questionnaires available that can screen for risk of sleep disorders including sleep apnoea, insomnia, body clock, sleep habits, and unrefreshing sleep.
Diary
The sleep diary is a classic way to get an overview of sleep and often will ask not just for the times in bed and whether it was good quality sleep, but it can also be used to record other things that would affect sleep such as work, exercise and caffeine consumption.
Self-report
If someone feels fatigued, too tired, unrefreshed by their sleep; this itself is a concern. Excessive sleepiness in the absence of an identifiable disorder is just as common as the most prevalent sleep disorders. With guidance, you may be able to identify some of the causes of sleepiness, possibly even some ways to improve it.
The best way to know if someone feels excessively sleepy is to ask!
