A wristwatch-type device that measures sleep and wake patterns over days or weeks.


A sense of paralysis that occurs between wakefulness and sleep, usually upon waking or sometimes at the onset of sleep. The person is conscious but cannot speak, move (cannot even open the eyes), and cannot breathe deeply. Atonia rarely lasts beyond 20 minutes, but when it first occurs, this experience can be terrifying, particularly if the patient also develops hallucinations.


Bi-level positive airway (BIPAP) pressure is similar to CPAP, but instead of one continuous pressure, there are two distinct pressure settings involved. One pressure is higher for inspiratory breathing and the second is a lower pressure for expiratory breathing. This helps ventilate an individual’s breathing and provides comfort, especially when high pressures are involved.


A common treatment for sleep apnea is Continuous Positive Airway Pressure (CPAP) therapy. CPAP works by pushing air through the airway passage at a pressure high enough to prevent apneas and can be prescribed for both obstructive and central sleep apnea.


A symptom characterized by the sudden loss of postural tone, often resulting in the individual falling to the floor. Cataplexy is often part of the narcolepsy complex.

Circadian rhythm

A rhythm that spans about a twenty-four-hour day, such as that of the sleep-waking cycle. Circadian rhythms in humans originate from a clock circuit in the hypothalamus that is set by information from the optic nerve about whether it is day or night. It is the normal sleep – wake cycle that allows the cyclical release of hormones and restoration of energy, and allows optimal body functions during the day.

EKG (electrocardiogram)

A test that records the electrical activity of the heart. It is of value for diagnosing cases of abnormal cardiac rhythm and myocardial damage. (see myocardium)

Epworth sleepiness scale (ESS)

A reliable scale used to assess daytime sleepiness and indicate the need to seek medical evaluation for sleep disorders. This is the same assessment tool used by sleep experts worldwide.


Elevated blood pressure or more commonly referred to as high blood pressure. Blood pressure is the force of blood pushing against the walls of arteries as it flows through them.


Dreams or hallucinations occurring just before sleep induced loss of consciousness.


Dreams or hallucinations persisting after sleep and before complete awakening.


A headache syndrome characterized by throbbing, usually one-sided pain, which may be associated with nausea, vomiting and visual disturbances.

Multiple sleep latency test

A sleep test that is used during a person’s normal wake periods during the day. It is used to evaluate excessive daytime sleepiness and narcolepsy (sudden and uncontrollable onsets of sleep).


The middle layer of the walls of the heart, composed of cardiac muscle.


A syndrome that is often hereditary, and characterized by repeated attacks of sudden sleep that may be associated with other specific abnormalities.


A sleep study that continuously measures and records a person’s physiological activity during a normal sleep period.

REM (rapid eye movement)

The stage of sleep that is characterized by decreased muscle tone, rapid eye movements and dreaming.

Sleep apnea

A disorder that results in cessation of breathing during sleep often due to obstruction of the upper airway.