The world of sleep science is filled with its own unique language. From "apnea" to "zeitgeber," understanding these terms can feel like learning a new subject. But knowing the vocabulary is the first step to better understanding your own sleep and having more informed conversations with your doctor.
This glossary is your quick-reference dictionary for the most common terms in sleep science. It's a great companion to our sleep calculator.
The A-Z Glossary of Sleep
Apnea: A temporary cessation of breathing during sleep. An "apnea event" is a key characteristic of sleep apnea.
Bruxism: The medical term for grinding or clenching your teeth during sleep. It can lead to jaw pain, headaches, and dental problems.
Chronotype: Your body's natural, genetically determined predisposition to sleep and wake at certain times. Learn if you're a Lion, Bear, or Wolf.
Circadian Rhythm: Your internal 24-hour body clock that regulates the sleep-wake cycle and other physiological processes. It is primarily influenced by light.
CPAP (Continuous Positive Airway Pressure): The gold-standard treatment for obstructive sleep apnea, involving a machine that uses mild air pressure to keep the airway open during sleep.
Delta Waves: The slow brain waves characteristic of deep sleep (NREM Stage 3). This is when your body does most of its physical repair work.
GABA (Gamma-Aminobutyric Acid): An inhibitory neurotransmitter that calms the nervous system and helps promote sleep. Many sleep aids, both natural and pharmaceutical, work by enhancing GABA's effects.
Hypnagogic Hallucinations: Vivid, dream-like hallucinations that occur as you are falling asleep. They are a common feature of sleep paralysis.
Hypnic Jerk: An involuntary twitch or sudden muscle contraction that occurs as you are falling asleep.
Insomnia: A sleep disorder characterized by persistent difficulty falling asleep, staying asleep, or getting quality sleep, leading to daytime impairment.
Melatonin: The "hormone of darkness," produced by the pineal gland in response to low light. It signals to the body that it's time to prepare for sleep.
NREM (Non-Rapid Eye Movement) Sleep: Comprises the first three stages of sleep, moving from light to very deep sleep. It is primarily associated with physical restoration.
Parasomnia: A category of sleep disorders that involve undesirable physical events or experiences that occur during sleep, such as sleepwalking, night terrors, or sleep-eating.
REM (Rapid Eye Movement) Sleep: The stage of sleep characterized by rapid eye movements, high brain activity, and vivid dreaming. It is crucial for memory consolidation and emotional regulation.
Restless Legs Syndrome (RLS): A neurological disorder characterized by an irresistible urge to move one's legs, typically during periods of rest at night.
Sleep Architecture: The structural organization of NREM and REM sleep stages throughout the night. A healthy sleep architecture shows predictable cycling through the stages.
Sleep Debt: The cumulative effect of not getting enough sleep. It's the difference between the amount of sleep you need and the amount you actually get.
Sleep Hygiene: The set of habits and practices that are conducive to sleeping well on a regular basis, such as maintaining a consistent schedule and creating a good sleep environment.
Sleep Inertia: The groggy, disoriented feeling upon waking that can last from a few minutes to a couple of hours. It's most severe when waking from deep sleep.
Zeitgeber: A German word meaning "time giver." It refers to any external cue that synchronizes an organism's internal body clock. The most powerful zeitgeber for humans is light.