Sleepis a naturally recurring state characterized by reduced or lacking consciousness, relatively suspended sensory and non-motor activity – inactivity of nearly all voluntary muscles.
It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, but it is more easily reversible than hibernation or coma.
Sleep is a heightened anabolic state, accentuating the growth and rejuvenation of the immune, nervous, skeletal and muscular systems. It is observed in all mammals, all birds, and many reptiles, amphibians, and fish.
The purposes and mechanisms of sleep are only partially clear and are the subject of intense research. Sleep is often thought to help conserve energy, but actually decreases metabolism only about 5-10%.
Hibernating animals need to sleep despite the hypometabolism seen in hibernation, and in fact they must return from hypothermia to euthermy in order to sleep, making sleeping “energetically expensive.”
Sleep debt is the effect of not getting enough rest and sleep; a large debt causes mental, emotional, and physical fatigue.
Sleep debt results in diminished abilities to perform high-level cognitive functions. Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure.
Scientists do not agree on how much sleep debt it is possible to accumulate; whether it is accumulated against an individual’s average sleep or some other benchmark; nor on whether the prevalence of sleep debt among adults has changed appreciably in the industrialized world in recent decades. It is likely that children are sleeping less than previously in Western societies.
Causes of difficulty in sleeping
There are many reasons for poor sleep. For example, excessive exposure to bright light within hours of bedtime or simply resisting the urge to fall asleep can trigger a “second wind,” which then can temporarily make it difficult to fall asleep afterwards.
Following sleep hygienic principles may solve problems of physical or emotional discomfort. When the culprit is pain, illness, drugs, or stress, the cause must be treated. Sleep disorders (including the sleep apneas, narcolepsy, primary insomnia, periodic limb movement disorder (PLMD), restless leg syndrome (RLS), and the circadian rhythm sleep disorders) are treatable.
Older people are more easily awoken by disturbances in the environment and may to some degree lose the ability to consolidate sleep.
Various patents, products, and sleep techniques exist as sleep aids, allowing a more natural position during sleep for better circulation and less body pain.
These methods range from returning to sleep on the floor since beds are a relatively recent invention in human history, to products which lift blankets off one’s feet to many kinds of “memory foam” which create a surface customized to an individual’s body position.