National Sleep Foundation

Glossary

R

Rapid Eye Movement (REM) Sleep - One of the three basic states of consciousness. An active period of sleep, marked by intense brain activity, rapid breathing, eye movement, and limb muscles paralysis. Most dreams occur during REM sleep.

Rapid Eye Movement Sleep Behavior Disorder (RBD) - A parasomnia in which the typical paralysis that characterizes REM sleep is weakened. People with RBD can act out their dreams, and risk injuring themselves and/or their bed partners.

Rebound (as in restless legs syndrome) - Occurrence or increase in prevalence or severity of symptoms in the morning resulting from withdrawal of a short-acting dopaminergic agent.

Recurrent Isolated Sleep Paralysis - A parasomnia characterized by an inability to talk or move either at sleep onset or upon awakening, while the person is fully conscious. IPS is also characterized by vivid hypnagogic hallucinations.

Relaxation Therapy - Used to treat insomnia by reducing movements and minimizing distracting thoughts, such as focusing on breathing, engaging in muscle relaxation, and meditating.

Respiratory Disturbance Index (RDI) - The number of apneas, hypopneas and Respiratory Effort-related Arousals (RERAs) divided by the hours of sleep.

Respiratory Effort-related Arousal (RERA) - Transient episodes of decreased inspiratory airflow or increased inspiratory effort lasting more than 10 seconds) leading to an arousal. The decreased respiration does not meet the criteria for either an apnea or hypopnea.

Respiratory Effort-related Arousal (RERA) - Transient episodes of decreased inspiratory airflow or increased inspiratory effort lasting more than 10 seconds) leading to an arousal. The decreased respiration does not meet the criteria for either an apnea or hypopnea.

Restless Legs Syndrome (RLS) - A neurological disorder that causes uncomfortable (and sometimes painful) tingling and tugging sensations in the legs. Symptoms usually intensify in the evening and at night, and can interfere with sleep.

Rhythmic Movement Disorder - A parasomnia characterized by repetitive, involuntary movements that occur during sleep, which can result in severe injury, Excessive Daytime Sleepiness, and other negative health outcomes.

Risk factor - Increases a person’s likelihood of developing a disease, experiencing a certain condition, or being injured. Common risk factors include age, gender, socio-economic status, genes, and lifestyle factors (i.e., diet, smoking, alcohol use).