symptoms. Insomnia can also be comorbid with or secondary to other disorders. Kleine–Levin syndrome, a rare disorder characterized by persistent episodic hypersomnia and cognitive or mood changes Narcolepsy, characterized by excessive daytime sleepiness (EDS) and so-called "sleep attacks," relatively sudden-onset, irresistible urges to sleep, which may interfere with occupational and social commitments. About 70% of those who have narcolepsy also have cataplexy, a sudden weakness in the motor muscles that can result in collapse to the floor while retaining full conscious awareness. Night terror, Pavor nocturnus, sleep terror disorder, an abrupt awakening from sleep with behavior consistent with terror Nocturia, a frequent need to get up and urinate at night. It differs from enuresis, or bed-wetting, in which the person does not arouse from sleep, but the bladder nevertheless empties. Parasomnias, disruptive sleep-related events involving inappropriate actions during sleep, for example sleepwalking, night-terrors and catathrenia. Periodic limb movements in sleep (PLMS), sudden involuntary movement of the arms and/or legs during sleep. In the absence of other sleep disorders, PLMS may cause sleep disruption and impair sleep quality, leading to periodic limb movement disorder (PLMD). Other limb movements in sleep, including hypneic jerks and nocturnal myoclonus. Rapid eye movement sleep behavior disorder (RBD), acting out violent or dramatic dreams while in REM sleep, sometimes injuring bed partner or self (REM sleep disorder or RSD) Restless legs syndrome (RLS), an irresistible urge to move legs. Shift work sleep disorder (SWSD), a situational circadian rhythm sleep disorder. (Jet lag was previously included as a situational circadian rhythm sleep disorder, but it does not appear in DSM-5, see Diagnostic and Statistical Manual of Mental Disorders for more). Sleep apnea, obstructive sleep apnea, obstruction of the airway during sleep, causing lack of sufficient deep sleep, often accompanied by snoring. Other forms of sleep apnea are less common. Obstructive sleep apnea (OSA) is a medical disorder that is caused by repetitive collapse of the upper airway (back of the throat) during sleep. For the purposes of sleep studies, episodes of full upper airway collapse for at least ten seconds are called apneas. Sleep paralysis, characterized by temporary paralysis of the body shortly before or after sleep. Sleep paralysis may be accompanied by visual, auditory or tactile hallucinations. It is not a disorder unless severe, and is often seen as part of narcolepsy. Sleepwalking or somnambulism, engaging in activities normally associated with wakefulness (such as eating or