The average person needs about seven to nine hours sleep each night. These are some of the sleep disorders that are keeping tens of thousands of UK adults awake or disrupting their sleep: Sleep Apnea: A disorder of breathing during sleep, typically accompanied by snoring, and causes the sufferer to wake up in order to breathe. There are two types: Obstructive sleep apnea is caused by an obstruction in the throat, a narrowing of the upper airway. Central sleep apnea is caused by a delay in the signal from the brain which controls breathing. Insomnia: Is a complaint about sleeping and includes difficulty falling asleep, difficulty staying asleep, and waking too early. Usually there is an underlying problem and this can involve a sleep disorder or something simple, such as drinking caffeine in the evening or being kept awake by stress. Insomnia can last a few nights to a few months, depending on the type, and needs to be diagnosed to allow the causes to be found and dealt with. Narcolepsey: Narcoleptics, no matter how much they sleep, continue to experience the need to sleep and can fall asleep while at work, talking, or driving a car. Known as 'sleep attacks', they can last from 30 seconds to more than 30 minutes. Suffers can also experience loss of muscle tone, ranging from a slight buckling at the knees to a complete limpness throughout the body. Restless leg syndrome: This is a discomfort in the legs which is relieved by moving or stimulating the legs. The feeling is described as a crawling, tingling or prickling sensation. Some medicines can help. Somnambulism (sleep walking): Caused by a series of complex behaviours initiated during sleep and usually starts during childhood. In its most severe form, sleep walking can take place almost nightly and end in physical injury. Sufferers are advised to seek help. Sleep Bruxism: Grinding or clenching of the teeth during sleep. Can be part of another sleep disorder and can cause damage to teeth. Seek help from a sleep clinic.