Sleep is a crucial component of maintaining good health, but understanding the intricate terminology associated with sleep can be challenging. The field of sleep science utilizes numerous technical terms, some with precise definitions to standardize usage among researchers and healthcare professionals, and others used more informally. This sleep dictionary aims to elucidate essential terminology, explain their meanings, and provide contextual insights into their usage, ensuring that readers can maximize the benefits of evidence-based resources by gaining a comprehensive understanding of vital aspects affecting their sleep.

In-depth coverage of sleep disorders is beyond the scope of this dictionary. Readers seeking information about sleep disorders are encouraged to visit our dedicated landing page, offering a general overview and links to comprehensive resources about specific conditions.

1. Actigraphy: Tracking the body’s movements over time, often achieved through wearable devices. Actigraphy helps measure various activities, including sleep duration.

2. Acute: Pertaining to short-term, sudden, or severe issues. In the context of sleep, it is used to differentiate from chronic conditions.
3. Arousal: A sudden transition from a deeper to a lighter stage of sleep or from sleep to wakefulness. Arousals in sleep studies are detected by changes in heart rate, breathing, or muscle activity.
4. Artificial Light: Light originating from sources other than the sun.
5. Aromatherapy: The use of specific fragrances to influence physical or mental health, promoting relaxation at night or alertness during the day in the context of sleep.
6. Atonia: A temporary paralysis of most muscles during rapid eye movement (REM) sleep, except those essential for breathing, pulse, and eye movement.
7. Awakenings: The act of waking up from any stage of sleep, often detected in sleep studies by changes in heart, lung, brain, and muscle activity.
8. Bad Dream: A dream with negative or bothersome content that does not cause awakening.
9. Bilevel Positive Airway Pressure (BPAP) Device: A device maintaining airway openness by delivering pressurized air through the mouth or nose, often used to treat obstructive sleep apnea.
10. Biphasic Sleep: A sleep pattern involving two sleep segments—typically, one at night and a nap during the day.
11. Blue Light: Light with a specific wavelength, often emitted by electronic devices, affecting circadian rhythm more than other wavelengths.
12. Chronic: Pertaining to long-lasting or ongoing conditions, often used to differentiate from acute issues in the context of sleep.
13. Circadian Rhythm: The body’s approximately 24-hour internal clock coordinating various physical and mental functions, including sleep.
14. Cognitive-Behavioral Therapy for Insomnia (CBT-I): A form of counseling targeting negative thoughts about sleep and encouraging healthier sleep habits, adapted to address insomnia.
15. Deep Sleep: The final stage of non-rapid eye movement (NREM) sleep characterized by the lowest levels of breathing and heart rate and specific brain wave patterns known as delta waves.
16. Delta Sleep: The NREM sleep stage marked by high-amplitude brain waves called delta waves, often known as stage 3, N3, deep sleep, or slow-wave sleep.
17. Dream: Mental imagery or thoughts occurring during sleep, most vivid during REM sleep.
18. Dream Recall: The ability to remember dream content upon waking.
19. Electroencephalograph (EEG): A test measuring brain activity using sensors on the scalp, aiding in identifying sleep cycle stages.
20. Entrainment: Synchronization of a person’s circadian rhythm with the daily light-dark cycle.
21. Excessive Daytime Sleepiness (EDS): A state of drowsiness or difficulty staying alert during the day.
22. Fatigue: A feeling of mental or physical energy depletion, often overlapping with excessive daytime sleepiness and cognitive impairment.
23. Hormones: Chemical messengers regulating various bodily functions, including those affecting sleep.
24. Insomnia: A sleep disorder characterized by difficulty falling or staying asleep despite the opportunity to sleep, leading to daytime impairment.
25. Insufficient Sleep: A state where the mind or body does not function optimally due to inadequate sleep duration or excessive sleep disruptions.
26. Jet Lag: A condition where the circadian rhythm is out of sync with the light-dark cycle due to rapid travel across multiple time zones.
27. Light Sleep: Commonly refers to stage 1 or N1 sleep, where a person is easily awakened.
28. Melatonin: A hormone regulating circadian rhythm and sleep, often supplemented to aid sleep.
29. Microsleep: Brief lapses into sleep, typically lasting a few seconds and associated with excessive daytime sleepiness.
30. Nap: A short sleep period, usually taken during the day, separate from the main sleep episode.
31. Nocturia: Frequent urination during the night.
32. Polysomnography: A specialized sleep study tracking multiple elements, including brain waves, muscle activity, and eye movement.
33. REM Sleep: The stage of sleep associated with intense dreaming and high brain activity.
34. Sleep Aid: A substance or medication used to improve sleep, including prescription drugs, over-the-counter medications, or dietary supplements.
35. Sleep Apnea: A sleep disorder characterized by disordered breathing, with obstructive sleep apnea and central sleep apnea being the main types.
36. Sleep Duration: The total time a person spends sleeping, measured for one sleep period or over a 24-hour day.
37. Sleep Hygiene: Individual habits and routines affecting sleep, encompassing the sleep environment setup.
38. Sleep Inertia: A drowsy or groggy feeling experienced shortly after waking up from sleep.
39. Sleep Onset: The process of falling asleep and initiating a sleep period.
40. Sleep Quality: An individual’s satisfaction with their sleep, considering aspects like initiation, maintenance, quantity, and feeling refreshed upon waking.
41. Sleep Regression: A deterioration of sleep in infants or toddlers after a period of improved sleep.
42. Sleep Stages: Distinct parts of the sleep cycle categorized into NREM and REM sleep, identifiable through changes in brain and body activity.
43. Sleeping Position: The physical posture adopted during sleep, including side, back, or stomach sleeping.
44. Slow-Wave Sleep: The third stage of NREM sleep, characterized by specific brain wave patterns.

45. White Noise: A noise containing sounds at all audible frequencies, often used to mask external noises during sleep.

This sleep terminology dictionary aims to demystify complex sleep-related terms, providing clear meanings and context to aid readers in understanding key sleep concepts and improve their sleep quality and habits. For detailed information on sleep disorders, readers are encouraged to explore dedicated resources offering comprehensive insights into specific conditions and treatments.