State the Disorders of sleep

The need for sleep varies considerably from one person to another, as well as in the same person at different stages of life. We have all been told that we need eight hours of sleep each night for good health. In fact, there are both long and short sleepers. Some people can stay healthy on as little as an hour of sleep per day, whereas others may need to sleep as much as 10 to 12 hours. The definition of what constitutes adequate sleep must be decided within the context of a person's sleep history. People who suffer from disorders related to sleep are usually examined in a sleep laboratory for 1 to 2 days. A polygraph (Poly meaning "many") records their brain waves, or EEG; an electromyogram, or EMG, records muscle activity; an electro oculogram, or EOG, records eye movements; and a thermometer measures body temperature during sleep. Together, these recordings provide a comprehensive and reliable description of sleep waking behaviour.