The term sleep disorder covers a wide range of conditions and symptoms. Sleep disorders can be broken down into various types.

• Primary sleep disorders. These aren't caused by another health or mental health condition.

• Secondary sleep disorders. These are the result of another health problem, such as depression, thyroid problems, stroke, arthritis, or asthma.

Types of primary sleep disorders

Primary sleep disorders can be divided into parasomnias and dyssomnias.

• Parasomnia sleep disorders. These cause abnormal activities during sleep, such as sleep terrors or sleep walking.

• Dyssomnia sleep disorders. These cause trouble falling asleep or staying asleep. Perhaps the most well-known dyssomnia is obstructive sleep apnea.

Other common dyssomnias are listed below.

Abnormalities of the central nervous system

Problems with the central nervous system can trigger a sleep disorder. Central sleep apnea occurs when breathing temporarily stops for 10 seconds or more many times during a night's sleep. This is caused by an abnormality in the brain. People with central sleep apnea breathe irregularly during sleep. This can result in low oxygen levels in the blood. This can worsen conditions such as epilepsy. Or it can lead to problems such as chest pain or heart attack in people who have coronary artery disease. Central sleep apnea may be caused by problems in carbon dioxide regulation.

Periodic limb movements in sleep (PLMS)

Periodic limb movements in sleep occur when the arms and legs move frequently and involuntarily during sleep. PLMS can cause the arms and legs to twitch, jerk, or flex. This can occur as often as a few times per minute for up to several hours. The cause of PLMS is unknown. But experts think it's likely related to the nervous system. PLMS can play a part in insomnia. It can cause daytime sleepiness and fatigue because the movements interrupt sleep.

Restless legs syndrome (RLS)

Restless legs syndrome is a nervous system disorder. It causes leg pain, a crawling feeling in the legs, or an urge to move the legs when you're trying to go to sleep. The symptoms tend to occur when you sit or lie down. They are relieved by walking or moving the legs. The symptoms are worse at night. RLS may make it hard to fall asleep or stay asleep. It also causes excessive sleepiness during the daytime.

Insomnia

This sleep disorder can be short term (acute). Or it can be long term (chronic). It can be linked to an outside cause, such as stress, medicine, or a health condition. When insomnia is the result of an outside cause, it's called secondary insomnia. Primary insomnia isn't caused by outside events. Its cause is not known. A healthcare provider may use an actigraph to help diagnose insomnia. An actigraph is a device you wear during sleep. It monitors your rest and activity cycles over a few days or weeks.

Here is more information about some types of insomnia:

• Psycho-physiological insomnia. This occurs when someone gets anxious about sleeping and focuses too intently on trying to sleep. In other words, the stress about sleeping itself causes insomnia.

• Paradoxical insomnia (formerly called sleep-state misperception). This is a sleep disorder marked by a significant difference between the time a person thinks they've been asleep and how much time they've actually slept. People with this problem may complain that they can't fall asleep. But they don’t have any problems during the day, even though they believe that they hardly slept. They are actually sleeping when they think they aren't. There's no evidence they have a sleep disorder.