Narcolepsy | Are You Constantly Tired, or Could It Be a Neurological Disorder?

Excessive Daytime Sleepiness (EDS) is the cardinal symptom of narcolepsy and the most disabling. It manifests as a persistent feeling of sleepiness, regardless of the amount of nighttime sleep obtained. This is not simple tiredness; it is an overwhelming, involuntary urge to sleep that can occur at any time, often during inappropriate situations such as while eating, talking, or driving. These episodes are often referred to as "sleep attacks." The underlying cause is a dysfunction in the brain's ability to regulate the sleep-wake cycle. Specifically, it involves a deficiency of hypocretin (also known as orexin), a neurotransmitter in the hypothalamus that promotes wakefulness. Without sufficient hypocretin, the boundaries between being awake and being asleep become blurred. As a result, elements of REM (Rapid Eye Movement) sleep, the dream stage of sleep, intrude into wakefulness. This neurological deficit means that the brain cannot maintain a consistent state of alertness, leading to uncontrollable lapses into sleep throughout the day. The severity of EDS can vary, but for many, it significantly impairs academic, professional, and social functioning, making it difficult to perform daily tasks that require sustained attention.

Cataplexy is a sudden and transient episode of muscle weakness triggered by strong emotions. While laughter is the most common trigger, other emotions such as excitement, anger, surprise, or fear can also induce an attack. Cataplexy is unique to narcolepsy with a hypocretin deficiency (Narcolepsy Type 1). The severity of muscle weakness varies widely among individuals. It can be subtle, such as a slight drooping of the eyelids or jaw, or it can be severe, causing a complete collapse of the body's voluntary muscles, leading the person to fall to the ground. Despite the physical collapse, the individual remains fully conscious and aware of their surroundings during the episode, which typically lasts from a few seconds to a couple of minutes. The physiological mechanism behind cataplexy is the inappropriate activation of the muscle atonia (paralysis) that normally occurs during REM sleep. In individuals with narcolepsy, this REM-associated muscle paralysis intrudes into the waking state in response to emotional stimuli.

Sleep paralysis is a temporary inability to move or speak that occurs when a person is falling asleep or waking up. This experience is essentially the muscle atonia of REM sleep continuing for a brief period after the mind has regained awareness. Hypnagogic hallucinations are vivid, dream-like experiences that occur at the transition from wakefulness to sleep. Their counterpart, hypnopompic hallucinations, occur upon awakening. These hallucinations can be visual, auditory, or tactile and are often frightening or bizarre. Both phenomena represent the intrusion of REM sleep characteristics into transitional states of consciousness.

Although individuals with narcolepsy experience excessive daytime sleepiness, their nighttime sleep is typically fragmented and of poor quality. The same neurological instability that causes sleep to intrude into the day allows wakefulness to intrude into the night. People with narcolepsy often experience frequent awakenings, vivid dreams, and periodic limb movements of sleep (PLMS). This disrupted nocturnal sleep does not alleviate daytime sleepiness and contributes to the overall burden of the disorder. The sleep architecture is abnormal, with individuals often entering REM sleep very quickly after falling asleep, a phenomenon known as sleep-onset REM periods (SOREMPs).

Diagnosing narcolepsy requires a comprehensive clinical evaluation and specialized sleep studies. The primary diagnostic tools are the polysomnogram (PSG) and the Multiple Sleep Latency Test (MSLT). The PSG is an overnight study that records brain waves (EEG), eye movements, muscle activity, heart rate, and breathing. It is used to rule out other sleep disorders, such as sleep apnea, that could be causing daytime sleepiness. The MSLT is performed on the day following the PSG. For this test, the individual is asked to take five scheduled naps, separated by two-hour intervals. The test measures how quickly the person falls asleep (sleep latency) and how many times they enter REM sleep during these naps. A diagnosis of narcolepsy is strongly indicated if the average sleep latency is less than eight minutes and there are two or more sleep-onset REM periods (SOREMPs). In some cases, measuring hypocretin levels in the cerebrospinal fluid can also confirm a diagnosis of Narcolepsy Type 1.