Narcolepsy is a specific neurological disorder that causes sudden attacks of deep sleep, while hypersomnia is a symptom, and refers to excessive daytime sleepiness more generally.

Hypersomnia and narcolepsy are related but distinct medical terms. Hypersomnia, or hypersomnolence, is a symptom of narcolepsy. It is therefore not possible to compare and contrast hypersomnia and narcolepsy, since they are not separate medical conditions.

But there are other causes for hypersomnia other than narcolepsy, and these conditions do have separate, distinctive features.

In this article, we will look at hypersomnia and narcolepsy in more detail, including what the terms mean and how they are related. We will also look at narcolepsy in comparison with some other causes of intense sleepiness.

A woman asleep on a train due to hypersomnia or narcolepsy. She is sat in the window seat with a newspaper partially covering her face.Share on Pinterest
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Hypersomnia, or hypersomnolence, is a medical term that describes excessive daytime sleepiness. It is a symptom rather than a medical condition.

A person with hypersomnia may need to sleep during the day or sleep for longer than average at night. People with this symptom may experience:

  • drowsiness or disorientation after waking up
  • the need for frequent napping
  • difficulty concentrating
  • difficulty remembering
  • slow speech

There are two categories of hypersomnia: primary and secondary. Primary hypersomnia occurs due to an underlying condition that directly affects the sleep-wake cycle, such as narcolepsy.

Secondary hypersomnia occurs when something else causes excessive tiredness, such as a medication, head injury, or health condition that disrupts sleep in other ways. For example, sleep apnea causes someone to temporarily stop breathing in their sleep, which lowers sleep quality and can cause daytime sleepiness.

Narcolepsy is a specific neurological disorder that causes sudden attacks of overwhelming sleepiness that can occur at any time. They may happen when someone is talking, eating, or driving. These attacks last a few seconds to a few minutes.

Narcolepsy is one of the causes of primary hypersomnia. But between attacks, people can have typical energy levels. People with narcolepsy also often experience:

  • sleep paralysis, which causes a temporary inability to move or speak as a person falls asleep or wakes up
  • hallucinations, which can accompany sleep paralysis and may be frightening
  • difficulty staying asleep at night, which may cause frequent waking or insomnia

People with type 1 narcolepsy also experience cataplexy, which is similar to fainting. Cataplexy causes a sudden loss of muscle tone and control when a person feels strong emotions. It may result in a total body collapse, or milder symptoms, such as sudden weakness or cataplexy in only one part of the body.

People with type 2 narcolepsy do not experience cataplexy.

What causes narcolepsy?

Scientists do not fully understand what causes narcolepsy. There may be different causes for types 1 and 2.

Almost all people with type 1 narcolepsy have very low levels of hypocretin, a chemical that keeps the body awake and regulates the rapid eye movement (REM) phase of sleep. This may explain why people with narcolepsy enter REM sleep much faster than most people, and why they can experience vivid dreams and sleep paralysis.

Researchers believe that people may develop type 1 narcolepsy if the cells that produce hypocretin die. This could happen due to an autoimmune disease, genetics, or environmental factors.

But those who have narcolepsy without cataplexy tend to have usual levels of hypocretin. The cause of type 2 is currently unknown.

Narcolepsy is one of the potential causes of primary hypersomnia, but there are others.

Idiopathic hypersomnia

Despite the name, idiopathic hypersomnia (IH) is a distinct medical condition named after its most prominent symptom. It is a disorder of the nervous system. Scientists do not understand what causes it, but the excessive tiredness and unrefreshing sleep it causes can be debilitating.

The symptoms include:

  • sleeping more than 10–11 hours a day
  • sleep that does not reduce tiredness
  • difficulty waking up, which may cause disorientation
  • mental fogginess and difficulty concentrating

Kleine-Levin syndrome

Another cause of primary hypersomnia is Kleine-Levin syndrome, a rare condition that causes episodes of excessive sleep that occur in cycles. The symptoms include:

  • sleeping up to 20 hours a day
  • excessive eating
  • behavior changes, such as having an unusually high sex drive or a lack of emotion
  • feeling confused, disorientated, or lethargic when awake
  • hallucinations

Between episodes, people can go for weeks or months with no symptoms. The condition often improves with age, but sometimes comes back when a person gets older. The cause of Kleine-Levin syndrome is unknown.

The following table compares narcolepsy with IH and Kleine-Levin syndrome:

IHNarcolepsyKleine-Levin syndrome
Main symptomgeneral and intense excessive sleepinessshort, sudden sleep attackscyclical episodes of excessive sleep
Sleep durationmany with IH sleep for more than 11 hours a day and may nap frequentlysleep attacks last a few seconds or minutesup to 20 hours a day during episodes
Impact on energy levelsoften severe, causing difficulty with daily taskscan be at usual levels between sleep attackssevere during episodes, but may return to usual levels for weeks or months in between
Sleep qualityoften very deep but unrefreshing, and does not alleviate tirednessoften disrupted by vivid dreams, sleep paralysis, or insomniavery deep during episodes
Age of onsetcan begin at any age, but usually develops in the mid-to-late teens or early 20scan begin at any age, but usually develops between childhood and early adulthood, from ages 7–25 yearsmainly occurs in male adolescents

The conditions that cause primary hypersomnia, including narcolepsy, are fairly rare. In many cases, excessive daytime sleepiness is the result of something else.

Some other causes for intense sleepiness include:

  • conditions that disrupt or lower sleep quality, such as sleep apnea
  • conditions that affect the brain or nervous system, such as Parkinson’s disease or brain injuries
  • conditions that impact mental health, such as depression
  • medications that cause sleepiness, such as antihistamines, opiates, and benzodiazepines

Learn more about the potential causes of excessive sleepiness.

Doctors can begin diagnosing the cause of excessive sleepiness by taking a medical history and asking questions about a person’s symptoms. They may also ask someone to keep a sleep diary for several days, so that they can get a better sense of how much a person sleeps, whether it is refreshing or not, and how this impacts their life.

Doctors also need to rule out other potential causes for the tiredness. They may look at any prescription or recreational drugs a person takes and order medical tests. If there is no clear cause, they can refer someone to a sleep laboratory.

There are two key tests a sleep laboratory can run:


A polysomnogram (PSG) records muscle and brain activity, eye movement, and breathing during sleep. This allows doctors to determine if REM sleep occurs earlier in someone’s sleep cycle than it should. It can also detect other causes for daytime sleepiness, such as sleep apnea.

Multiple sleep latency test

A multiple sleep latency test looks at daytime sleepiness. The day after a PSG, a person must take five short naps, each separated by 2 hours. On average, falling asleep in 8 minutes or less is an indication of excessive daytime sleepiness.

For narcolepsy testing, in some cases, a doctor may also measure the level of hypocretin in the fluid surrounding the brain and spinal cord. But because low hypocretin levels are not characteristic of type 2 narcolepsy, it is not always useful.

The treatment for hypersomnia depends on the cause. For hypersomnia caused by narcolepsy, doctors may prescribe medications to help prevent daytime sleep attacks. This may include:

  • Wake-promoting medications: Modafinil (Provigil) is the first-line treatment for narcolepsy. It is a non-stimulant wake-promoting medication. This class of drug is derived from amphetamines, but causes fewer side effects and is less likely to cause addiction.
  • Stimulants: Sometimes, doctors may prescribe stimulants. But these amphetamine-like drugs can cause a number of side effects, and can be addictive. Examples include dextroamphetamine (Dexedrine) and methylphenidate (Ritalin).
  • Antidepressants: Several types of antidepressant are effective for controlling cataplexy. These include tricyclic antidepressants, selective serotonin reuptake inhibitors, and serotonin and norepinephrine reuptake inhibitors.
  • Sodium oxybate: This drug can also treat cataplexy and hypersomnia in people with narcolepsy. Sodium oxybate is a highly controlled substance because of how potent it is.

In 2021, the Food and Drug Administration (FDA) approved sodium oxybate for use in people with IH. Currently, it is the only drug officially approved for the condition. But because the treatments for narcolepsy can also help with IH, many doctors prescribe them for off-label use.

Managing hypersomnia often involves making lifestyle changes. These may include:

  • maintaining a consistent schedule for activity, rest, and sleep
  • exercising daily for at least 20 minutes, and at least 4–5 hours before sleep
  • avoiding heavy meals before sleep
  • practicing relaxation before bedtime
  • stopping smoking, especially at night
  • avoiding caffeine and alcohol

People with primary hypersomnia can also seek additional support in the workplace, at home, and for their mental health. This may include:

  • workplace adjustments to allow for naps and a flexible schedule, which people with narcolepsy are entitled to under the Americans with Disabilities Act
  • treatment with a therapist to help with the impact hypersomnia has on a person’s mood
  • support groups for others experiencing the same symptoms or conditions
  • a service animal who can wake someone up in emergencies or help with tasks

It is also important for people with hypersomnia to take safety precautions. This may mean avoiding certain activities when feeling sleepy, such as driving, walking up or down stairs, or operating machinery.

Hypersomnia refers to excessive daytime sleepiness. In people with narcolepsy, this manifests as short, sudden sleep attacks, which cause an overwhelming urge to sleep during daily activities. People with narcolepsy can also experience cataplexy, sleep paralysis, vivid dreams, and hallucinations.

Other causes for hypersomnia include IH, Kleine-Levin syndrome, certain medications, and other medical conditions that indirectly affect sleep. Only a doctor or sleep specialist can diagnose the cause.

Excessive sleepiness has a significant impact on quality of life, but treatments and strategies can help minimize the symptoms. If someone is experiencing persistent sleepiness during the day, and getting enough sleep does not help, they should speak with a medical professional.