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, although once aware of it, sufferers tend to be woken up by their own groaning as well. 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 occurs during REM sleep, although it may also occur to a lesser degree during NREM sleep. Often the groaning occurs toward the end of the sleep cycle, within a couple hours of waking. In many cases it occurs exclusively during REM sleep. Catathrenia begins with a deep inspiration. The sufferer holds 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.