Narcolepsy, which is classified as a sleep disorder, causes a patient to exhibit a strong, even uncontrollable, urge to sleep during the daytime. Narcoleptics experience what are called "sleep attacks," episodes of deep sleep that come upon them suddenly while they're engaged in other activities such as work or school.
While the sleeping may be misunderstood as voluntary in nature, or a psychological problem, it has a physical origin in the central nervous system. Narcolepsy represents an inability to control the sleep-wake cycle so that normal separation of the sleeping and waking periods occurs. Sleeping and waking are fragmented experiences rather than continuous sequences.
The American Sleep Foundation estimates the number of Americans with narcolepsy at between 125,000 and 200,000, but also notes that less than 50,000 of those people have received an accurate diagnosis, because narcolepsy is often confused with mental or emotional problems, or with seizure disorders.
Symptoms of Narcolepsy
Excessive Daytime Sleepiness and Sleep Attacks
All narcoleptics experience the condition known as excessive daytime sleepiness (EDS), and that symptom is the one most commonly associated with this disorder. The word narcolepsy comes from two Greek root words meaning "stupor" and "seizure," which put together convey the idea of the irresistible onset of intense drowsiness that occurs.
When the narcoleptic falls asleep during the day, that happens very fast and without warning. The patient enters REM sleep with abnormal speed (as little as five minutes, as opposed to one hour for a normal person). Those sleep attacks can last only a few seconds, for several minutes, or occasionally as long as one hour.
The sleep attack is in no way affected by what the patient is doing, which means it is inadvisable for a narcoleptic to drive or operate heavy machinery. Fortunately, the patient usually awakes feeling physically refreshed, with some hope of remaining active for the next few hours. However, the characteristic sudden awakenings can produce disorientation, even dizziness, if they interrupt a period of REM sleep.
Moving in and out of sleep at an accelerated pace can cause confused thinking, unhappiness, an absence of energy, and a feeling of fatigue. Anyone who has trouble waking in the morning will easily understand how taxing and disruptive it would be to have to do that not once, but many times each day while trying to complete other tasks.
Nighttime Sleep Disturbances
In narcolepsy, none of the patient's sleep patterns are normal ones. Thus, when trying to sleep at night, the patient frequently wakes up, and displays excessive physical movement while still asleep. The stages of sleep do not proceed in their regular order, because the patient goes into REM sleep very fast, instead of entering sleep gradually (the usual pattern is light sleep first, REM sleep last in the sleep cycle).
That leads to a deficit of deep sleep, which is what causes the EDS.
Cataplexy means a sudden inability to control the muscles, caused by a loss of tone or tension in the skeletal muscles (atonia) that permits the muscles to stretch without resistance. That relaxation causes muscular weakness and loss of voluntary muscle control, and can include limp muscles in the legs and arms, slurring in speech, or a drooping neck. Those visible symptoms cause cataplexy to be mistaken for an epileptic seizure, although the patient's consciousness remains unimpaired and no loss of memory occurs.
Depending on how many muscles are affected and how long the cataplectic attack persists, it may go unnoticed by observers, or it may produce what looks like a fainting fit when the patient loses the ability to stand upright. The trigger for cataplexy is sometimes not apparent, but feeling or expressing strong emotions is known to stimulate cataplectic fits. The unexpected onset of fear, anger, excitement, or even laughter can result in cataplexy.
In cataplexy, the muscular atonia resembles that which is a normal part of REM sleep, and researchers believe the same neurons in the patient's brain are responsible for both effects. That means the disruption of the sleep cycle found in narcolepsy includes not just abnormal ordering of the stages of sleep (which is usually a unified and predictable sequence), but also abnormal timing of the physical characteristics of REM sleep, which occur unpredictably in the narcoleptic.
The hallucinations found in narcolepsy are called either hypnagogic (occurring when the patient begins to sleep) or hypnopompic (happening while the patient is awake). The hallucinations are often described as vivid in nature and frightening in content. The content is primarily visual, but other sensory impressions are frequently reported also.
These hallucinations can take place in the setting of wherever the patient happens to be at the time, which makes them particularly realistic. About half of all known narcolepsy patients have them. They are very like the dreams found in REM sleep, and are thought to be another REM event that happens at the wrong time.
In sleep paralysis, which occurs when the narcoleptic is trying to transition between sleeping and waking, the patient cannot move or speak because of voluntary muscle inhibition. As in the case of cataplexy and hypnagogic hallucinations, the temporary paralysis is a normal concomitant of REM sleep, but it creates a very frightening effect when the narcoleptic is still conscious during the experience.
Sleep paralysis can last for about 15 minutes.
Automatic behavior means the narcoleptic, while in the state of consciousness associated with sleep, continues to perform routine tasks associated with waking. But the lack of conscious control is often apparent.
For example, a narcoleptic might start making nonsensical conversation, or if engaged in taking notes, the notes may be illegible or unintelligible. Or the narcoleptic may do something silly like placing laundry in the refrigerator.
Causes of Narcolepsy
The Role of Hypocretins
Researchers are only beginning to understand exactly how narcolepsy works. It is believed that certain neurons in the brain, called hypocretin neurons, are affected by an autoimmune disorder that causes the body's immune system to target them for attack. When enough hypocretin neurons have been destroyed, there's a shortage of the neurotransmitters called hypocretins, which they normally secrete.
Hypocretins (also known as orexins) help regulate and stabilize wakefulness and suppress REM sleep. When there is a hypocretin deficiency, the patient slips in and out of wakefulness rather than maintaining that state in the usual fashion.
Genetic Conditions Affecting Narcolepsy
Various genetic traits have been found to occur more frequently in narcoleptics, and while this line of research is relatively new, some linkages are already known to exist. Genes controlling the production of human leukocyte antigen (HLA), specifically the HLA-DR15 and HLA-DQ6 gene variants, are found in many narcoleptics.
Since antigens can provoke the type of autoimmune attack thought to kill the patient's hypocretin neurons, that finding is particularly relevant.
There are several different parts of the brain which interact to control sleeping and waking, and tracing the genetic determination of all the physical structures involved will be a tremendously complex endeavor. A few narcoleptics are known to possess a genetic variation that interferes with the processing of hypocretins, and it is certain more genetic factors will be discovered eventually.
Injury to the part of the brain known to control REM sleep, including tumors and diseases, has been identified as a cause of narcolepsy.
Effects of Narcolepsy
Fortunately, there are almost no physical problems directly caused by narcolepsy itself. Since hypocretins also help control food intake, the hypocretin deficiency can result in obesity, which is often associated with narcolepsy, but other than that effects are confined to the extreme inconvenience of uncontrollable sleeping.
It would be very difficult to overstate the hindrance that falling asleep at any time of day, in the middle of any activity imaginable, can present in the narcoleptic's life. Having a medical problem that is mistaken for a behavior problem, a mental illness, or a seizure disorder is quite unpleasant in and of itself.
But if you think about what it would be like to experience a period of sudden sleep while driving, or a period of automatic behavior during a timed test which produced written answers that made no sense, and then imagine facing those challenges on a daily basis, you'll have some faint idea of the hardships narcoleptics undergo.
See our page on treating narcolepsy for more information.