Note! This section continues a schematic overview of select sleep disorders. Consult a sleep specialist if you believe that you are a candidate for any of the disorders described on this sleep education platform.

Other Sleep and Arousal Disorders


The disorder that we will discuss in the category of hypersomnias of central origin is narcolepsy. The hypersomnia disorders are those in which the primary complaint is daytime sleepiness (defined as the inability to stay alert and awake during the major waking episodes of the day, resulting in unattended lapses into sleep). In narcolepsy, excessive daytime sleepiness is debilitating and consists of repeated lapses into sleep episodes across the day. Patients typically sleep for a short duration and awaken refreshed, however, sleepiness occurs again within a few hours. Sleepiness is more likely to occur during activities that require little physical and cortical arousal, such as watching television. Sleep attacks are sudden and often irresistible due to their involuntary origins. We will see that the best way to conceptualize narcolepsy is by considering it an unwelcome flicking of a switch in the brain to turn on sleep (or rather, to turn off wake). In narcolepsy, sleep is not completely turned on however, only key portions, thus the switch is faulty.

Hypocretin, also known as orexin is the important mediator in the sleep-wake switch, but it is deficient in narcolepsy. The disorder is characterized by unique conditions apart from excessive daytime sleepiness, including cataplexy and vivid hallucinations.

Before we look at these two bizarre phenomenon we should note a quick word about sleep-onset in the form of a switch. In the main Circadian Rhythm and Sleep Architecture learning sections, we outline the critical structuring of sleep, and we discussed how that structure is embedded in a larger circadian rhythm cycle. We emphasize that sleep onset requires sleep preparatory hormones to be active on multiple fronts, and that the entire circadian rhythm ebb-and-flow structure that includes sleep within it does not run on 'master clock' oscillations alone, but has need to be synchronized with external cues such as light and darkness, as well as many of our consistent behaviors. All of this appears quite contrary to the notion of simple sleep and wake "switches" that can be augmented pharmacologically. When it comes to sleep onset, however, all of that preparatory work and critical internal functioning after sleep onset still requires a set of switch-like mechanisms.

Cataplexy is a medical condition in which strong emotion or laughter causes a person to suffer sudden physical collapse even though they remain conscious. It is a unique characteristic of narcolepsy and the sudden loss of muscle tone is often provoked by strong emotions that are often positive— such as laughter, pride, elation or surprise. Cataplexy may be localized to regions such as the lower limbs, neck, mouth or eyelids or it may include large skeletal muscle groups. Affected areas commonly include the knees, face, and neck. Respiratory muscles are not affected in cataplexy. Remember also that the respiratory muscles remain in tact during dream, so narcolepsy can be conceptualized as a form of REM-like episodes that intrude into the day through bad "switches". The duration of cataplexy is usually short, ranging form a few seconds to several minutes. Recovery is immediate.

Sleep paralysis and hypnagogic hallucinations (hallucinations occurring immediately prior to sleep onset) along with nocturnal sleep disruption commonly occur in patients with narcolepsy. The hypnagogic hallucinations are vivid perceptual experiences typically occurring right at sleep onset and can occur even for persons without narcolepsy if they are sufficiently sleep-deprived (as can accompanying sleep paralysis). These hallucinations are often accompanied by a realistic awareness of the presence of someone or something else in the room, and include visual, tactile, kinetic, and auditory phenomena. The accompanying feeling may be one of fear or dread that an intruder means harm but paralysis does not allow one to react. Because of this collection of specific and unique phenomenology, it has been often proposed that sleep paralysis and hypnagogic hallucinations are the basis for "alien abduction" intreprations from people who were either positive for narcolepsy and did not know it, or undergoing a period of severe sleep deprivation (which can invoke similar phenomenon).

For proper diagnosis, physicians ensure that the cause of the primary symptom must not be disturbed sleep from other sleep disorders or medical conditions, or a misaligned circadian rhythm, but due to "central" sleep-wake biological mechanisms. Other sleep disorders may be comorbid with a final diagnosis, but they must first be appropriately treated before the diagnosis is confirmed. The narcolepsy "tetrad" is below.

Excessive Sleepiness

Daytime sleepiness is excessive, debilitating and occurs repeatedly



Much like 'fainting' from strong emotions; with no loss of consciousness


Sleep Paralysis

Temporary paralysis of muscles other than respiratory apparatus



Vivid, perceptually real experiences with fear of "presence" in room


The parasomnias consist of abnormal sleep-related movements, behaviors, emotions, perceptions, dreaming, and autonomic nervous system functioning. We outline a few important parasomnias below.

REM Behavior Disorder (RBD) is an abnormal set of behaviors that occur in REM sleep and may result in injury and subsequent sleep deprivation. A complaint of sleep related injury is common with RBD because subjects attempt to physically enact an unpleasant, active, or violent dream outwardly. Basic REM mechanisms that are designed to actively paralyze skeletal muscle during dreaming (sparing the muscles required for respiratory breathing) malfunction. Because the physical environment of our dream does not correspond to the internal dream environment, injuries are likely when skeletal muscle is not inhibited and the person acts out dream mentation in the real physical environment. An association between RBD and narcolepsy has been made. In addition, evidence from basic research is suggestive that RBD may precede Parkinson’s Disease.


Confusional arousals are characterized by mental confusion or confusional behavior that occurs during or after arousal from sleep. These arousals are common in children and can occur in both nocturnal sleep and daytime naps.

Sleepwalking is a series of complex behaviors that occur after sudden arousals from slow-wave sleep (SWS) and result in locomotor behavior in a state of altered consciousness that is similar to sleep. Our common language seems to imply that sleepwalking is a form of a ‘dream state’ behavior, however, sleepwalkers can appropriately navigate the real physical environment in a near sleep state. Sleepwalking is not, therefore, a form of dream state, because the landscape of dream would not correspond to the actual physical environment that sleepwalkers navigate without the mismatch that is presented in RBD.
Sleep Terrors also occur from near SWS and are associated with a cry or a piercing scream. The patient experiences autonomic level emotions of terror, including intense fear. The autonomic emotional response is thought to be due to activation of portions of the amygdala and other associated regions of the brain that instantiate fear. The fear is not mediated by cognitive thoughts or dream mentation, but occurs outside of REM stage dream sleep. Effectively, the experience of fear is turned on during deep slow-wave sleep, without the context of a mental thought or situation. Because the parasomnia occurs outside of dream mentation, it also bears a confusional aspect. Children exhibiting sleep terrors are hard to arouse and exhibit subsequent amnesia about the event soon after. Contrary to the soothing inquiries from parents, they do not report ‘nightmare’ storylines because the episode is associated with deep dreamless unconscious sleep. Sleep terrors and sleep walking may co-occur.

Recurrent Sleep Paralysis can occur at sleep onset or upon awakening from sleep. It is characterized by an inability to perform voluntary movements, however, ventilation is unaffected. Hallucinatory experiences often accompany temporary paralysis.  Diagnosis requires the absence of narcolepsy as sleep paralysis is a component of narcolepsy. Severe sleep restriction or deprivation may cause symptoms of sleep paralysis during sleep onset or upon awakening. These episodes are transient and unlike narcolepsy.

Movement Disorders

The sleep-related movement disorders are characterized by relatively simple, usually stereotyped movements that often repeat and disturb sleep.

Restless Legs Syndrome (RLS)

RLS is characterized by an irresistible urge to move the legs often accompanied by uncomfortable or painful symptoms. The sensations are worse at rest and occur more frequently in the evening or during the night (exhibiting a circadian component). Walking or moving the legs relieves the symptoms. RLS is not the same as cramping, compression or other chronic musculoskeletal conditions in the legs or limbs. The urge is often difficult to articulate, but its ramping up of a "necessity" to repeatedly move the limb is the defining feature, not the fact that there is discomfort or pain in the limb/legs.

RLS patients may also experience accompanying periodic limb movements during sleep that comprise periodic limb movements of sleep (PLMs). The PLMs limb movements in RLS patients are often associated with frequent arousals from sleep and may occur in up to 80% to 90% of patients with RLS, however RLS is a movement disorder that radically interferes with sleep onset as opposed to periodic limb movement disorder which presents frequent micro-arousals during sleep.

Severe RLS may progressively shorten sleep time to five hours or less per night. Increased rates of depression and anxiety are reported with RLS patients. RLS treatment consists of levodopa or dopamine-receptor agonists to address the motor and sensory features of the disorder. Iron, dopamine, and genetics appear to be primary factors in the RLS pathology. Iron deficiency increases the risk for RLS. Several medications have been reported to precipitate or aggrevate RLS, including dopamine-receptor antagonists, many antidepressants and sedating antihistamines.

In contrast to RLS, positional discomfort, which can occur from compressive pressure on nerves, is sometimes confused with RLS, however, the discomfort is resolved by changing body position without requiring any continued body movement. The discomfort does not include an irresistible urge to move the legs. RLS patients often have difficulty describing both the urge and the sensations.

Sleep-related leg cramps
are also worse at night, relieved by movement, and in some cases, interpreted as an urge to move. However, leg cramps always involve muscle hardening or muscle pain that requires stretching of the muscle, not strictly movement, to relieve the underlying urge. Following movement, leg cramps will have residual pain and tightness that is unresponsive to movement, whereas RLS symptoms are relieved and no longer manifest during movement.

Periodic Limb Movement Disorder (PLMD)

PMLD, though consisting of the stereotypical periodic limb movements of sleep (PLMs) that are highly probable in RLS patients, is a separate disorder of sleep and does not present the same symptom set that RLS does to interrupt sleep onset. PLMD requires separate diagnostic criteria (an overnight PSG study) because the symptoms manifest during sleep. PLMs occur most often in the lower extremities and involve extension of the big toe in combination with partial flexion of the ankle, the knee, and sometimes the hip. Movements may be vigorous and associated with an autonomic or cortical arousal during each repetitive sequence (often hundreds per night). Typically, the patient is unaware of the limb movement or the micro-arousals and report only unrefreshing sleep and/or excessive daytime sleepiness. (See the Sleep Architecture section of this platform to understand why unrecognized micro-arousals can translate into serious consequences).

Other Disorders

Sleep-Related Bruxism. Bruxism, or “tooth grinding” is an oral activity characterized by clenching or grinding of the teeth during sleep, usually accompanied by arousals. Jaw contractions can either come in the form of isolated and sustained clenching (tonic contractions), or a series of repetitive (phasic) contractions termed rhythmic masticatory muscle activity (RMMA). The condition can lead to abnormal wear of the teeth, tooth pain, jaw muscle pain, or temporal headache. Temporomandibular joint pain with limited joint movement may also accompany sleep-related bruxism.

Interestingly, individuals who are highly motivated or characteristically maintain high vigilance may have an increased prevalence of sleep-related bruxism. Precipitating factors may include anxiety related to current life events or tasks requiring high levels of performance, in the context of difficult deadlines.


There are many other Disorders of Sleep & Arousal. Use the Locator below to contact a sleep center in your area if you suspect that you or someone you love suffers from a sleep disorder.

The current healthcare structure seeks to utilize primary care physicians as the gateway to treatment of common disorders such as OSA, including screening, diagnostics and oversight of OSA treatment compliance. But although primary care physicians are increasingly aware of the adverse cardiometabolic and psychological impacts associated with sleep disorders such as OSA, PCP's are not trained specifically in sleep disorders. If you need to find a sleep specialist associated with a sleep center, you can use the sleep center locator from the American Academy of Sleep Medicine (AASM): locator.

Sleep Is Not Rest.

Although Nourish Sleep is a non-clinical entity, we do not operate outside of a responsible care pathway. Nourish Sleep screening does not constitute confirmation of a sleep disorder or lack thereof. Only a face-to-face clinical evaluation with a clinician or board certified sleep physician can affirm the necessity for further diagnostics or treatment. Our role is to educate you and provide you a rigorous, but highly tailored and comprehensive understanding of your specific sleep quality. Although we work collaboratively with a diverse array of clinical and educational resources to fulfill that mission, Tri-Nourish Inc and Nourish Sleep constitute non-clinical entities offering non-clinical services. Our goal is to assist your sleep quality in a pre-pathological (preventative) approach that takes into consideration domains that impact health and wellbeing before they transition into common sleep, mental or physiological disorders. Poor sleep quality radically impacts productivity, performance, health, emotional resilience, and safety— well before the sleep disorder threshold has been breached.