Sleep and sleep disorders.

Sleep is a complex neurological state, with its primary function of providing rest and restoring the body's energy levels. The importance of sleep could be seen from the fact that people spend about one-third of their lifespan in sleep. Normal human sleep is divided into non-rapid eye movement (NREM) and rapid eye movement (REM) sleep, and the alteration between NREM and REM occurs about 4-5 times during a night of normal sleep. Human NREM sleep could be classified into four stages, namely, stage I, II, III and IV, representing successively deeper stages of sleep. Sleep is an active rhythmic neural process produced by several brain areas, of which the preoptic and other basal forebrain areas play a major role in the generation of NREM sleep. Interaction of the pedenculo-pontine and lateral dorsal tegmental areas with the dorsal raphae nucleus and locus coeruleus, is important for REM sleep generation. Suprachiasmatic nucleus of the hypothalamus and the pineal gland ensure that sleep and wakefulness follow a circadian periodicity of nearly 24 hours. Alterations in the quality, quantity and pattern of sleep result in sleep disorders. Persistent and repeated interruption of sleep affects the health of an individual. Undiagnosed and untreated wake/sleep complaints cause not only misery to the sufferer, but it also has socio-economic consequences. Sleep disorders cover a wide spectrum of diseases. Though there are more than 100 identified sleep/wake disorders, most sleep complaints can be categorised into five, namely, hypersomnia, insomnia, circadian rhythm disorders, parasomnias, and sleep disorders associated with mental, neurological, and other medical disorders. Researches during the last 50 years, and the advances made in clinical sleep medicine, have lead to more effective treatments for the myriad human sleep disorders. It is not possible to assign a specific reason for many of the sleep disorders, but some aspects of sleep and wakefulness are genetically influenced. But, most commonly, sleepiness during waking hours, results from volitional or forced sleep deprivation during previous nights, due to social, economic and environmental reasons. So, public awareness about sleep disorders should be an essential part of any programme aimed at global management of sleep disorders.