In addition to how much sleep one gets, recent research has shown that the timing of sleep is also crucial to one’s overall wellbeing.

In the United States alone, 50 to 70 million people experience some type of chronic sleep disorder, according to the American Academy of Sleep Medicine (AASM). These include:

• Breathing disorders

One billion people worldwide are thought to suffer from obstructive sleep apnea, in which the airway gets blocked for short periods, breathing stops, and less air reaches the lungs, increasing the risk for cardiovascular disease.

Less common is central sleep apnea, a potentially fatal disorder in which breathing stops and starts unpredictably because the brain isn’t working properly.

•  Insomnia

About one in three US adults report trouble falling asleep or staying asleep, or waking up too early and not falling back to sleep, according to the American Psychiatric Association.

Worldwide, the prevalence of insomnia ranges from 10% to 60%.

• Excessive sleepiness

Conditions where people oversleep, and fall asleep at inconvenient or dangerous times – such as while driving – are known as hypersomnias. Causes range from a lack of a chemical in the brain that regulates wakefulness to seasonal changes: in winter, there is less sunlight sending wake-up signals to the brain.

Sleeping too much – more than nine hours per night on a regular basis, according to the AASM – can also be a sign of underlying health problems.

• Parasomnias

Parasomnias are unwanted events that occur while a person is sleeping. People with parasomnias might move, talk, and express emotions while appearing to be awake, even though they are really asleep.

• Movement disorders

Among the best known is restless legs syndrome, in which sufferers feel a burning or itching in their legs when they lie down. Others include painful leg cramps in the middle of the night, uncontrollable muscle movements, and bruxism – the grinding or clenching of the teeth.

What happens if you lack sleep?

The importance of getting enough sleep is supported by decades of research. The amount we need can vary from person to person, but guidelines from the US National Sleep Foundation recommend seven to nine hours every night for ages 18 to 64, and seven to eight hours per night for older adults.

Sleep deprivation has been shown to cause cognitive impairment akin to that seen when drunk. The longer we are awake, the worse our reaction times, short-term memory, and logical reasoning become, similar to what happens as blood alcohol content (BAC) increases.

For adults, being awake for 17 hours is similar to having a BAC of 0.05%, a level at which driving impairments are seen, according to the US National Institute for Occupational Safety and Health. Some countries use this level as a cutoff for legal intoxication.

One American study of more than 6,800 road accidents found that drivers who slept less than four hours the night before an accident were 15 times more likely to be at fault than those who had slept at least seven hours.

Absolute sleep deprivation can be fatal. Inadequate sleep affects everything from the immune system to muscle tone.

Costs of insufficient sleep

The economic costs of poor sleep are enormous. On an individual level, it leads to reduced productivity, decreased concentration and focus, and increased workplace absenteeism or presenteeism.

Sleep-deprived people are also more likely to make mistakes, be less efficient, and experience a decline in cognitive abilities, which can affect their performance and prospects.

On a larger scale, poor sleep can also have significant medical costs, sending more people to seek healthcare and take medication, and leading to increased medical errors.

Other costs include increases in traffic and industrial accidents, injuries, and decreased workplace productivity and economic competitiveness. A 2019 study found that insufficient sleep reduces voting and other behaviours that are beneficial to society.

Researchers from the Rand Corporation calculated in 2016 that the US loses an equivalent of about 1.23 million working days annually due to insufficient sleep, corresponding to about 9.9 million working hours.

Annual losses for other countries were estimated to average 0.6 million working days in Japan, and 0.2 million days each in the United Kingdom and in Germany.

Rand economists also estimated that the US was sustaining an annual economic loss related to insufficient sleep of US$280 billion to US$411 billion, or up to 2.28% of the overall economy.

Japan, they estimated, was losing up to almost 3% of its economy to insufficient sleep, followed by the UK and Germany.

How to sleep better

Good sleep habits will obviously contribute to better slumber. These include going to bed and waking up at roughly the same time every day, and making sure your bedroom is quiet, dark, relaxing and a comfortable temperature.

Other routines can also help, such as being physically active during the day and avoiding heavy meals, caffeine and alcohol before bedtime.

Other measures include talking therapies such as cognitive behavioural therapy, light therapy, physical appliances to keep the nose and throat clear, as well as surgery and medication. Lifestyle modifications and weight loss are sometimes recommended as well.