Catathrenia is a rapid eye movement sleep parasomnia consisting of end-inspiratory apnea (breath holding) and expiratory groaning during sleep. Catathrenia is distinct from both somniloquy and obstructive sleep apnea. The sound is produced during exhalation as opposed to snoring which occurs during inhalation. It is usually not noticed by the person producing the sound but can be extremely disturbing to sleep partners. Bed partners generally report hearing the person take a deep breath, hold it, then slowly exhale; often with a high-pitched squeak or groaning sound.

Catathrenia typically, sometimes even exclusively, occurs during REM sleep, although it may also occur to a lesser degree during NREM sleep. Catathrenia begins with a deep inspiration. The sufferer holds her or his breath against a closed glottis, similar to the Valsalva maneuver. After a period of time and some blood oxygen desaturation, there is an arousal, followed by expiration. Expiration can be slow and accompanied by sound caused by vibration of the vocal cords or a simple rapid exhalation with no sound.

There is debate about whether the cause is physical or neurological, a question that requires further study. While some speculate about a direct correlation to high anxiety and stress or the concept that catathrenia is purely psychological, there is only anecdotal evidence of either proposed cause.

Catathrenia has been defined as a parasomnia in the International Classification of Sleep Disorders Diagnostic and Coding Manual (ICSD-2), but there is debate about its classification.

There are a few other similaritiesamongst catathrenia sufferers that have not yet been studied properly:

- Many catathrenia sufferers mention that they also suffer from some form of stress or anxiety in their lives.

- Sufferers themselves do not feel like they are experiencing a sleep apnea; the breath-holding appears to be controlled though the unconscious. Oxygen desaturation during a catathrenia episode is usually negligible.

- Many took part in sports activities during teens and twenties some which required breath-holding which included many types of sports such as swimming and even weight lifting. They find a certain level of comfort in breath-holding, and often do it while awake.

- Observations have been made of instances of breath holding during daily activities that require concentration.

- Some sufferers recalled suffering from lucid or stress dreams during their catathrenia episodes during their sleep.

- Some sufferers complain of having a painful chest upon waking from sleep.

Because catathrenia itself is not considered life-threatening, there has been very little research done in the medical community, and many experts assume that the way to treat catathrenia is to treat the underlying sleep apnea, though there is no conclusive evidence published that catathrenia results from sleep apnea, and sleep studies show that not all sufferers of catathrenia have been diagnosed with sleep apnea.

While doctors tend to dismiss it as an inconvenience, sufferers routinely describe the condition's highly negative effects on their daily lives including tiredness, low energy, dizziness and vertigo, work problems, relationship and social issues, and other physical and mental problems that could be associated with low sleep quality.

Sleeping in a more upright position seems to lessen catathrenia (as well as sleep apnea). Performing regular aerobic exercise, where steady breathing is necessary (running, cycling etc.) may lessen catathrenia. Strength exercise, on the other hand, may worsen catathrenia because of the tendency to hold one's breath while exercising. Yoga and/or meditation focused on steady and regular breathing may lessen catathrenia.

Recurrent Isolated Sleep Paralysis is an inability to perform voluntary movements at sleep onset, or upon waking from sleep.

Histamine plays a role in wakefulness in the brain. An allergic reaction over produces histamine causing wakefulness and inhibiting sleep Sleep problems are common in people with allergic rhinitis. A study from the N.I.H. found that sleep is dramatically impaired by allergic symptoms and that the degree of impairment is related to the severity of those symptoms s Treatment of allergies has also been shown to help sleep apnea.

According to one meta-analysis, the mean prevalence rate for North America and Western Europe is estimated to be 14.5±8.0%. Specifically in the United States, the prevalence of restless leg syndrome is estimated to be between 5 and 15.7% when using strict diagnostic criteria. RLS is over 35% more prevalent in American women than their male counterparts.

REM sleep behavior disorder or RBD is the most common REM sleep parasomnia in which muscle atonia is absent. This allows the individual to act out their dreams and may result in repeated injury—bruises, lacerations, and fractures—to themselves or others. Patients may take self-protection measures by tethering themselves to bed, using pillow barricades, or sleeping in an empty room on a mattress.

Demographically, 90% of RBD patients are males, and most are older than 50 years of age.

Typical clinical features of REM sleep behavior disorder are:

- Male gender predilection

- Mean age of onset 50–65 years (range 20–80 years)

- Vocalisation, screaming, swearing that may be associated with dreams

- Motor activity, simple or complex, that may result in injury to patient or bed-partner

- Occurrence usually in latter half of sleep period (REM sleep)

- May be associated with neurodegenerative disease

Acute RBD, occurs mostly as a result of a side-effect in prescribed medication—usually antidepressants. But if not then 55% of the time the cause is unknown the other 45% the cause is associated with alcohol.

Chronic RBD is idiopathic, meaning of unknown origin, or associated with neurological disorders. There is a growing association of chronic RBD with neurodegenerative disorders—Parkinson's disease, multiple system atrophy (MSA), or dementia—as an early indicator of these conditions by as much as 10 years.

Patients with narcolepsy also are more likely to develop RBD.