What is a nervous disorder whereby a person suddenly falls asleep?

Option D

Narcolepsy is a sleep disorder characterized by excessive sleepiness, sleep paralysis, hallucinations, and in some cases episodes of cataplexy (partial or total loss of muscle control, often triggered by a strong emotion such as laughter). Narcolepsy occurs equally in men and women and is thought to affect roughly 1 in 2,000 people. The symptoms appear in childhood or adolescence, but many people have symptoms of narcolepsy for years before getting a proper diagnosis.

People with narcolepsy feel very sleepy during the day and may involuntarily fall asleep during normal activities. In narcolepsy, the normal boundary between awake and asleep is blurred, so characteristics of sleeping can occur while a person is awake. For example, cataplexy is the muscle paralysis of REM sleep occurring during waking hours. It causes sudden loss of muscle tone that leads to a slack jaw, or weakness of the arms, legs, or trunk. People with narcolepsy can also experience dream-like hallucinations and paralysis as they are falling asleep or waking up, as well as disrupted nighttime sleep and vivid nightmares.

Narcolepsy with cataplexy is caused by the loss of a chemical in the brain called hypocretin. Hypocretin acts on the alerting systems in the brain, keeping us awake and regulating sleep wake cycles. In narcolepsy, the cluster of cells that produce hypocretin—located in a region called the hypothalamus—is damaged or completely destroyed. Without hypocretin, the person has trouble staying awake, and also experiences disruptions in the normal sleep-wake cycles.

Currently there is no cure for narcolepsy, but medications and behavioral treatments can improve symptoms for people so they can lead normal, productive lives.

Narcolepsy is diagnosed by a physical exam, taking a medical history, as well as conducting sleep studies. If you do have narcolepsy, the most effective treatment is often a combination of medications and behavioral changes. People who are diagnosed with narcolepsy should seek counseling through educational networks and support groups. Getting a diagnosis of narcolepsy and managing the symptoms can be overwhelming and the disorder is not well understood by the general public. It helps to learn best practices and access support through others who have the disorder.