Sleep-wake disorders cause a number of sleep disturbances that affect the amount, quality, or timing of sleep or that induce abnormal events during sleep. Some sleep-wake disorders are serious enough to interfere with normal physical, mental, and emotional functioning. Disruptions in sleep can be caused by a variety of issues, from teeth grinding (bruxism) to night terrors. Polysomnography is a technique that can be used to identify some sleep disorders. 

Insomnia Disorder

Insomnia refers to a chronic difficulty in falling asleep and/or maintaining sleep when no other cause is found for these symptoms. It is often a symptom of a mood disorder (e.g., emotional stress, anxiety, depression), an underlying health condition (e.g., asthma, diabetes, heart disease, pregnancy, or a neurological condition), or abuse of alcohol or drugs. However, it can also be a disorder in its own right.

The DSM-5 diagnostic criteria for insomnia disorder are as follows:

• The person experiences dissatisfaction with sleep quantity or quality as a result of difficulty initiating or maintaining sleep.
• As a result the person experiences clinically significant distress or impairment in social, occupational, educational, academic, behavioral, or other important areas of functioning.
• The sleep difficulty occurs despite adequate opportunity for sleep.
• The sleep difficulty occurs at least 3 nights per week.
• The sleep difficulty is present for at least 3 months.

The DSM-5 also provides the following exclusion criteria:

• The insomnia must not be better explained by and must not occur exclusively during the course of another sleep-wake disorder (e.g., narcolepsy, a breathing-related sleep disorder, a circadian rhythm sleep-wake disorder, a parasomnia).
• The insomnia must not be attributable to the physiological effects of a substance (e.g., a drug of abuse, a medication).
• Coexisting mental disorders and medical conditions must not adequately explain the predominant complaint of insomnia.

Hypersomnolence Disorder

Hypersomnolence disorder (also known as idiopathic hypersomnia) is a disease of likely neurological origin that is characterized primarily by severe, excessive daytime sleepiness. It has been diagnosed only rarely and is often very difficult to diagnose at an early stage. It is usually a debilitating lifelong disease. There is a very low level of public awareness of this disorder, which often results in stigmatization of those who suffer from it. Currently, there is no cure, there are no FDA-approved treatments, and research funding for the study of this disorder is scarce.

Narcolepsy

Narcolepsy is also referred to as excessive daytime sleepiness (EDS). Individuals with this disorder often fall asleep spontaneously but unwillingly at inappropriate times. People with narcolepsy tend to have trouble in areas such as work, leisure, and personal relationships.

Narcolepsy

Narcolepsy is characterized by an individual uncontrollably falling asleep very suddenly, typically in inappropriate situations.

Breathing-Related Sleep Disorders

Some sleep disorders are caused by disturbances in breathing. Sleep apnea, for example, is a disorder in which obstruction of the airway during sleep causes a lack of sufficient deep sleep, often accompanied by snoring.

Sleep apnea is usually caused by some sort of physical condition that obstructs the breathing system, such as obesity, rather than a mental condition. The DSM-5 names two types of sleep apnea: obstructive sleep apnea, in which your airway collapses during sleep, and central sleep apnea, in which your brain does not signal your lungs to continue to inhale.

Individuals with sleep apnea often feel tired throughout the day, as the constant breaks in their sleep cycle cause unrestful nights.

Parasomnias

Parasomnias are a category of sleep disorders that involve abnormal movements, behaviors, emotions, perceptions, and dreams that occur while falling asleep, while sleeping, while between sleep stages, or during arousal from sleep. Most parasomnias are due to partial arousal during the transitions between wakefulness and non-rapid-eye-movement (N-REM) sleep or between wakefulness and rapid-eye-movement (REM) sleep.

Sleepwalking (Somnambulism)

Sleepwalking (sometimes called sleepwalking disorder, somnambulism, or noctambulation) causes a person to get up and walk during the early hours of sleep. The person may sit up and look awake (though they're actually asleep), get up and walk around, move items, or dress or undress themselves. They will have a blank stare and still be able to perform complex tasks. Some individuals also talk while in their sleep, saying meaningless words and even having arguments with people who are not there. A person who sleepwalks will be confused upon waking up and may also experience anxiety and fatigue.

Sleepwalking can be dangerous—people have been known to seriously hurt themselves during sleepwalking episodes. It is most common in children, but it also occurs occasionally in adults. For adults, alcohol, sedatives, medications, medical conditions and mental disorders are all associated with sleepwalking.

Sleep Terrors and Nightmare Disorder

Sleep terrors are characterized by a sudden arousal from deep sleep with a scream or cry, accompanied by some behavioral manifestations of intense fear. Sleep terrors typically occur in the first few hours of sleep, during stage 3 NREM sleep. Night terrors tend to happen during periods of arousal from delta sleep (i.e., slow-wave sleep). They are worse than nightmares, causing significant disorientation, panic, and anxiety. They can last up to 10 minutes, and the person may be screaming and difficult to wake. In adults, it is often a symptom of some psychopathology.

Distinct from sleep terrors is nightmare disorder. Also known as "dream anxiety disorder," nightmare disorder is characterized by frequent nightmares. The nightmares, which often portray the individual in a situation that jeopardizes their life or personal safety, usually occur during the second half of the sleeping process, called the REM stage. Though many people experience nightmares, those with nightmare disorder experience them more frequently.

Restless Legs Syndrome

Restless legs syndrome (RLS) is a neurological disorder characterized by an irresistible urge to move one's body to stop uncomfortable or odd sensations. It most commonly affects the legs, but it can also affect the arms, torso, head, and even phantom limbs. Moving the affected body part modulates the sensations, providing temporary relief. RLS may start at any age, including childhood. For some it is a progressive disease; for others the symptoms decrease over time.