Specialist expertise: Sleep Disorders, Sleep Apnea, Sleep, Respiratory Medicine, Lung Health.
The amount of sleep a person requires is genetically determined. Families tend to sleep for the same amount of time. The average sleep requirement is 8.1 hours every 24 hours although the range is from 6 hours to more than 10 hours. Put another way 50% of us need more than 8 hours! It is not possible to alter this requirement.
Insomnia is not simply short sleep which might be normal for the individual but rather that there is an impact of this short sleep on daytime functioning, which is one of the harmful effects. Those who need less than the usual amount of sleep because of the genes would function quite normally in the day.
Thus insomnia is a subjective complaint of difficulty getting to sleep, staying asleep or sleep that is unrefreshing but importantly with daytime consequences. Reasons for this lack of sleep are many including alterations of the body clock which delay sleep onset. This is called Delayed Sleep Phase Syndrome. The genetic underpinnings of this are well understood with one of the 10 clock genes having alterations which lead to a delay in the drive to sleep.
There can also be conditions which disturb the continuity of sleep. The common ones are those related to snoring and interrupted breathing, and repetitive limb jerking. It perhaps goes without saying that psychiatric disturbances have a big impact on sleep with depression and anxiety being the main issues.
However, the most common form of insomnia is a learned behaviour. This is a factor behind the development of some difficulty sleeping in one third of the population at some point in the year. This one third of the population has a measurably different physiology in terms, for example, of increased levels of cortisol and adrenaline which allow that person, that physiology, to be more arousable. Another consequence of this hyper-aroused state is that in spite of the lack of sleep there is a tendency not to be sleepy in the day. Importantly, for one third of that one third of the population that is one in 10, the problem persists, because it can.