Sleep is vital for a variety of bodily functions. We spend about 30% of our lives asleep, and without it, death occurs in a few days. It is possible to survive longer without food than sleep. Sleep affects both psychological and physiological parameters. Lack of it, or disruption of it by sleep disorders, obviously affects sleepiness, but also has important consequences on fatigue, vigilance, mood, learning and memory, as well as motor coordination. It also affects immune function, cardiac rhythm, blood pressure, hormonal function, sensitivity to pain, liability to seizures. There is increasing evidence of its role in heart disease, risk of stroke and risk of dementia.
Sleep requirement is largely defined by your genes, and also whether your sleep is disrupted by any sleep disorders. Everyone has a slightly different sleep requirement, but as a general rule, most people need between seven and eight hours a night. If you are lying in for more than an hour or so on days that you are not working, this suggests you are not sleeping enough.
Sleep disorders are categorised into the hypersomnias, parasomnias and insomnias. Insomnia is very frequent, affecting 20-30% of the population in any one year. Furthermore, about 20% of the population is sleep-deprived simply due to not spending enough time in bed. The hypersomnias describe sleep disorders that cause excessive daytime sleepiness. The commonest of these is obstructive sleep apnoea, snoring with obstruction of the airway, affecting about 4-8% of adult men, and a slightly lower proprotion of women. This is a frequent cause of road accidents due to falling alseep at the wheel of a car. Other conditions that can cause excessive sleepiness include neurological disorders such as restless legs syndrome/periodic limb movement disorder, affecting about 2% of the adult population, and conditions such as narcolepsy, affecting 1 in 2000 to 3000 people. Narcolepsy causes profound sleepiness, vivid dreams, sleep paralysis, hallucinations as you drift into our out of sleep, and cataplexy, the sudden loss of muscle strength, usually precipitated by strong emotion. The parasomnias describe conditions that cause abnormal behaviours such as sleep-walking, night terrors and REM sleep behaviour disorder (acting out of dreams).
If you or your partner are having disrupted sleep, or you are excessively sleepy during the day, you should seek medical attention. High blood pressure that is not responding to drug treatment should raise the possibility of sleep apnoea.
Sleep is divided into two categories of sleep. Normal sleep is described as non-REM. This is the part of sleep that is primarily restorative. REM sleep is the stage of sleep in which we dream, and our muscles, except those that allow us to breathe and move our eyes, are paralysed. The function of dreaming is not precisely understood, but it is thought to have an important role in learning and memory.
Generally people who are lacking in sleep are sleepy during the day, whereas those with insomnia have trouble sleeping at night but also trouble sleeping during the day. While there are consequences to insomnia such as psychological issues and fatigue, sleepiness is not one of them. At present, we are not clear if the physiological consequences are different.
There is a clear gender effect, in that women are much more likely to suffer from insomnia than men. Some of this is likely to be due to psychological differences, but we are also aware that restless legs syndrome is commoner in women due to hormonal effects and due to women being more likely to have low iron levels, a risk factor for restless legs syndrome.
Keep your bed for sleeping. Don’t work, use a computer or watch TV in bed. Avoid exposure to bright light in the evenings – this lowers melatonin levels, your brain’s signal that it is time to go to sleep. Avoid caffeine after mid-afternoon. Exercise in the day, not directly before you go to bed. Avoid large carbohydrate-rich meals before bedtime – this can cause fluctuations in blood sugar levels at night. Avoid excess alcohol – this can disrupt sleep directly, but also causes bladder distension at night and can worsen sleep apnoea. Try to keep your hours of sleep regular.
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