Bruxism: grinding one's teeth while asleep.

Circadian rhythm: the daily fluctuation of physiological or behavioral functions that include sleep-wake states generally tied to the 24-hour daily dark-light cycle.

Continuous Positive Airway Pressure (CPAP): a device that delivers pressurized air into the nose and helps keep the throat open to reduce pauses in breathing.

Gastroesphageal Reflux Disease (GERD): the flow of stomach acid upwards into the esophagus, which can cause arousals and disrupt sleep.

Hypersomnia: sleeping for uncharacteristically long periods of time.

Hypersomnolence: excessive daytime sleepiness.

Hypnotics: sleep-inducing drugs.

Jet lag: disturbances in circadian rhythm caused by rapid travel across multiple time zones. Symptoms include sleep disruptions and impaired alertness.

Insomnia: a common sleep problem characterized by: trouble falling asleep, waking frequently during the night, waking too early and can't get back to sleep.

Light therapy: used to treat Seasonal Affective Disorder (SAD) and other conditions that may result from reduced exposure to light. It involves exposing the eyes to light of appropriate intensity and duration at the appropriate time of day to adjust the timing, duration and quality of sleep. Light alters the secretion of melatonin by the pineal gland.

Melatonin: a hormone secreted by the pineal gland in the brain, produced at night, in darkness, and brings on the urge to sleep.

Narcolepsy: a chronic neurological disorder that involves the body's central nervous system. A major symptom of narcolepsy is excessive and overwhelming daytime sleepiness.

Nightmares: unpleasant and/or frightening dreams occurring in REM sleep. Night terrors are characterized by an incomplete arousal from slow wave sleep. If awakened during a night terror, the individual is usually confused and, unlike a nightmare, doesn't remember details of the event.

NREM: or slow wave sleep consists of sleep stages 1 through 4 and is characterized by a gradual decrease of mental activity, body temperature, heart rate and blood pressure. We spend about 75% of sleep time in NREM state.

Parasomnias: a wide range of disruptive sleep-related events characterized by full or partial arousal from sleep. They include sleep walking, sleep-related eating, night terrors and bruxism (teethgrinding).

Periodic Limb Movement Disorder (PLMD): periodic episodes of repetitive limb movements during sleep.

Polysomnogram or diagnostic sleep study: monitors and records a variety of body functions during sleep such as electrical activity of the brain, eye movement, muscle activity and heart rate. The study is used to diagnose sleep disorders such as sleep apnea.

REM (Rapid Eye Movement) Sleep: The sleep state in which vivid dreaming occurs. About 25 percent of sleep is REM sleep, which first occurs about 90 minutes after falling asleep and is characterized by a shut down of muscles, relaxed bodies, irregular breathing and heart rate.

REM Sleep Behavior Disorder: characterized by the lack of muscle paralysis during REM sleep, during which the individual acts out the ongoing dream.

Restless Legs Syndrome (RLS): a neurological movement disorder characterized by unpleasant tingling, crawling, creeping and/or pulling feelings in the legs causing an urge to move in order to relieve the symptoms and resulting in difficulty in falling and staying asleep.

Sleep: The state in which an individual rests quietly in a recumbent position, disengages from the environment, and becomes unresponsive to stimuli.

Sleep apnea: a serious, potentially life threatening condition characterized by pauses in breathing during sleep. Sleep apnea may be associated with irregular heartbeat, high blood pressure, heart attack, and stroke. It is treated with a mask-like device called a CPAP, continuous positive air pressure, which fits over the nose and mouth and pumps air into the throat to keep air passages open.

Sleep deprivation: an insufficient amount of sleep or poor sleep due to difficulty sleeping, disruptions and/or a sleep disorder. Sleep deprivation can have a negative impact on a person's mood, behavior and performance.

Sleep hygiene: behavioral activities that contribute to or detract from restorative sleep. Examples of good sleep hygiene include activities such as going to bed at the same time each night, restricting caffeine and alcohol intake near bedtime.

Snoring: caused by a partial obstruction to the air passage that causes the tissue to vibrate resulting in a snoring noise. Snoring can be a symptom of sleep apnea, a serious sleep disorder characterized by pauses in breathing during sleep.