Disruptive sleep-related disorders are called parasomnias. Parasomnias are characterized by undesirable physical or verbal behaviors, such as walking or talking during sleep. They occur during specific stages of sleep.
There are two categories of Parasomnias:
1. Primary parasomnias: disorders of sleep states. They are further classified according to whether or not they occur during the REM stage of sleep (rapid eye movement stage, which means the eyes move rapidly and dreaming occurs) or the non-REM stage (non–rapid eye movement stage, which means eye movement does not take place).
2. Secondary parasomnias: disorders of other organ systems that can take place during sleep. For example, seizures (convulsions), respiratory dyskinesias (difficulty in performing respiratory movements), arrhythmia's (abnormal heart rhythms), and gastroesophageal reflux (food or liquid regurgitating from the stomach into the foodpipe).