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Narcolepsy is a sleep disorder in which the sufferer does not have normal patterns of sleeping and waking.  Narcoleptics experience aspects of REM sleep at unusual times, during the day as well as at night.

Most people enter REM sleep after going through four stages of NREM sleep.

Someone with narcolepsy, on the other hand, will enter REM sleep as soon as they fall asleep. They will also enter REM sleep frequently during the day, when they are expected to be fully awake. A person with narcolepsy may also experience the paralysis, loss of muscle tone and hallucinations that characterize REM sleep at unusual times.

The most noticeable symptom of narcolepsy is excessive daytime sleepiness, or EDS.  People with narcolepsy may fall asleep suddenly in unusual situations, for example, while eating or in the middle of a conversation.

Narcoleptics often suffer from sleep paralysis.  Although many people who do not have narcolepsy have experienced sleep paralysis at some time in their lives, narcoleptics have frequent sleep paralysis attacks.  During normal REM sleep, your body's large voluntary muscles become paralyzed, so you do not act out your dreams.  During sleep paralysis, you retain this characteristic of REM sleep, but you are conscious and aware that you are paralyzed.

Cataplexy, or loss of muscle tone, is a symptom of narcolepsy. Loss of muscle tone is also associated with REM sleep.  An attack of cataplexy takes place when the narcoleptic is awake, and is often triggered by strong emotions. A cataplectic attack can range from slurred speech or weakness in the knees to a complete collapse that is followed by paralysis.

Hypnagogic hallucinations and hypnopompic hallucinations are also common in people with narcolepsy, although anyone may experience them. Hypnagogic hallucinations are hallucinations that you experience while you are falling asleep, while hypnopompic hallucinations are hallucinations that you experience while you are waking up.

A 2010 study suggests that narcoleptics frequently have lucid dreams, and that narcoleptics are more likely to recall disturbing dreams than people without narcolepsy.

Sometimes a person with narcolepsy may fall asleep for less than a minute. (This is known as a microsleep.) During this time, they may perform routine activities, such as typing or cleaning, without being conscious of what they are doing.  This is known as automatic behavior. After the narcoleptic awakens from their microsleep, they may not remember their automatic behavior.

While narcoleptics may fall asleep at unusual times during the day, they may also suffer from insomnia, as their sleep patterns are disturbed.  People with narcolepsy may awaken frequently during the night.

People with narcolepsy may suffer from REM Sleep Behavior Disorder (RBD). When they dream, their voluntary muscles may not be completely paralyzed, and they may act out their dreams.  Most people with RBD are elderly men. However, it is about as common in women with narcolepsy as it is in men with narcolepsy.  In narcoleptics, symptoms of RBD tend to appear around middle age.   RBD can be one of the first symptoms of narcolepsy in a child.

People with narcolepsy are more likely to suffer from sleep apnea than the general population.

Narcoleptics are more likely to be overweight or obese than people without narcolepsy. They are more likely to be overweight or obese than people with idiopathic hypersomnia (excessive sleepiness with no discernible cause), which indicates that their weight gain is not entirely caused by lack of activity.

Binge eating tends to be common in narcoleptics.

Narcolepsy can affect mammals other than humans, such as dogs, cats, mice and rabbits.

Causes of Narcolepsy

People with narcolepsy tend to have low levels of neurons that produce a neurotransmitter known as hypocretin, or orexin, which helps to keep you in a waking state. Hypocretin is found in spinal fluid.

Some scientists believe that narcoleptics suffer from an immune disorder that causes these neurons to be destroyed.

A virus may cause narcolepsy in some individuals.

Narcolepsy has a genetic component; there are certain genes which are much more common in narcoleptics than in people without narcolepsy. However, people with narcolepsy usually do not have other family members with narcolepsy. This indicates that the environment plays a strong role in the development of narcolepsy.

Diagnosis of Narcolepsy

A number of different methods are used to diagnose narcolepsy

If a doctor suspects that you have narcolepsy, he may ask you to fill out the Epworth Sleepiness Scale, a questionnaire that reveals how sleepy you are during the day.

You may have to keep a sleep diary, in which you keep track of when you are awake and when you are asleep, for one or two weeks

While you are keeping your sleep diary, your doctor may ask you to wear a device, known as an actigraph, which resembles a wristwatch and monitors your sleep patterns.

You may have to go to a sleep lab, where you will be given a polysomnogram (PSG), also known as a sleep study.  During a polysomnogram, you will sleep with sensors attached to you. Some of these sensors record your brain activity. They will be used to determine when you enter REM sleep.

During a polysomnogram, your muscle activity, breathing, heart, rate, blood pressure and blood oxygen levels will also be measured.

The PSG will determine if you have narcolepsy and are entering REM sleep too early. It will also reveal if something other than narcolepsy is making you fall asleep during the day - for example, if you have sleep apnea or periodic limb movement disorder.

After your polysomnogram, you may have to remain at the sleep lab for a multiple sleep latency test (MSLT) which is used to determine how quickly you fall asleep, and how quickly you enter REM sleep, during the day.

During a multiple sleep latency test, you will be asked to rest in a quiet room for about half an hour while your brain activity is measured. You will be asked to do this four or five different times during the day.

You may also be given a test to measure the level of hypocretin in your spinal fluid.

Dangers of Narcolepsy

People who have narcolepsy that is not controlled are at risk from accidents caused by not being alert or awake in potentially dangerous situations, for example, when cooking or when driving.

Falling asleep during the day at unexpected times can make it difficult for a narcoleptic to do well in school, to keep a job or to maintain a relationship.

People who suffer from cataplexy may avoid experiencing intense emotions, which can make it difficult for them to relate to others.

Fear of a having an attack of cataplexy when outside can cause some narcoleptics to develop agoraphobia.

All of these things can cause someone with narcolepsy to suffer from depression.

Treatment of Narcolepsy

Narcoleptics are often prescribed stimulants, which help them to stay awake during the day.

However, these stimulants may cause them to have difficulty sleeping at night, which can ultimately make daytime sleepiness worse.

Narcolepsy is sometimes treated with a drug known as sodium oxybate, also known as GHB or Xyrem. This medication can improve nighttime sleep, reduce daytime sleepiness and prevent cataplexy.

SSRIs (selective serotonin reuptake inhibitors), such as Paxil, Prozac and Zoloft, and SNRIs (selective norepinephrine reuptake inhibitors), such as Effexor, are prescribed to narcoleptics in order to prevent cataplexy, sleep paralysis, and hypnagogic and hypnopompic hallucinations.  SSRIs and SNRIs suppress REM sleep.  These drugs are used to treat depression as well as narcolepsy.  Depression is associated with excessive REM sleep.

Tricyclic antidepressants, such asTofranil, help to prevent cataplexy.

If you have narcolepsy, it can help to schedule daytime naps for yourself.  Napping may make you feel less sleepy during the day.

Getting some exercise every day, but not too close to bedtime, can help to regulate your sleep patterns.

Some narcoleptics have service dogs, who can help when their owners are feeling very drowsy or confused, or when their owners have attacks of cataplexy.

For more information about the stages of sleep, see What Happens When We Sleep and Dream?