The language of military sleep science.
Plain-language definitions grounded in the clinical and regulatory literature.
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
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A
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Adenosine
A molecule that accumulates in your brain during waking hours, creating the pressure to sleep. The longer you’re awake, the…
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Alertness Management
The systematic use of behavioral and pharmacological tools to maintain safe levels of wakefulness and cognitive function in…
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Amygdala
An almond-shaped brain region that processes emotional significance, especially threat. It plays a central role in fear memory…
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Apnea-Hypopnea Index (AHI)
A measurement of how many times per hour your breathing becomes blocked (apnea) or significantly reduced (hypopnea) during…
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Autonomic Nervous System
The part of your nervous system that works on autopilot, controlling heart rate, digestion, breathing, and blood vessel…
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Backward Rotation
A shift schedule that moves earlier each rotation: nights, then evenings, then days. Generally harder to adapt to than forward…
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Blue-Light Blocking
A circadian intervention using amber-tinted lenses that filter visible light at wavelengths below approximately 530nm,…
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Brainstem Sleep Circuits
Networks deep in the brain that control sleep stages and muscle paralysis.
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Bright Light Therapy
Structured daily exposure to high-intensity artificial light (typically 10,000 lux for 20-60 minutes), timed to shift the…
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Caffeine Half-Life
The time required for your body to eliminate 50% of the caffeine you consumed. For most adults this is 5-6 hours — but it can…
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Caffeine Nap
Drinking caffeine immediately before a 15-20 minute nap. Caffeine takes ~20 minutes to act, so it kicks in just as you wake…
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Cataplexy
A sudden loss of muscle tone triggered by strong emotion, usually laughter or surprise. The person stays conscious but cannot…
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CBT-I (Cognitive Behavioral Therapy for Insomnia)
A structured 6-8 session psychological treatment for chronic insomnia that addresses the thoughts and behaviors perpetuating…
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Chronobiological Adaptation
The process of resetting your circadian clock to a new schedule, whether from time-zone travel, shift work, or operational…
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Chronotype
Your natural preference for morning or evening activity — whether you’re a ‘morning lark’ who bounces out of bed at 6 AM or a…
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Circadian Entrainment
The process by which your body’s internal clock synchronizes to the outside world, primarily through light exposure.
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Circadian Low
The portion of your 24-hour clock when your body is biologically pushed toward sleep, typically between roughly 2 AM and 6 AM.…
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Circadian Misalignment
A state where your internal body clock is out of sync with your external schedule — or where different organs within your body…
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Circadian Rhythm
Your body’s internal 24-hour cycle that controls when you feel awake, sleepy, hungry, and alert. It runs even without external…
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Circadian Watchbill
A circadian watchbill is a watch schedule designed to align duty rotations with the human circadian system — specifically,…
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Clock Genes
The genes that run your internal 24-hour clock. They turn each other on and off in a feedback loop that takes about a day to…
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Cognitive Fatigue
Decline in mental performance from sustained cognitive effort or sleep loss. Different from physical fatigue; not always…
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Compensation and Pension Exam (C&P Exam)
A Compensation and Pension (C&P) exam is a medical examination requested by the VA to evaluate a veteran’s disability claim.…
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Comprehensive Fatigue and Endurance Management Policy (CFEMP)
The Comprehensive Fatigue and Endurance Management Policy (CFEMP) is a US Navy surface fleet policy mandated by fleet…
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Core Body Temperature
The temperature of your body’s internal organs and blood, as opposed to your skin temperature. Core body temperature follows a…
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Cortisol
A steroid hormone produced by the adrenal glands that follows a strong circadian rhythm, surging in the morning (the cortisol…
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CPAP (Continuous Positive Airway Pressure)
A therapy that uses a bedside machine to deliver steady air pressure through a mask, keeping your airway open during sleep.
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CYP1A2
The liver enzyme that breaks down caffeine. Genetic variation in CYP1A2 explains why some people can drink coffee at 8 PM and…
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D
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Deployment-Related Sleep Disorder
Sleep disturbance that develops during or after military deployment, often combining insomnia, nightmares, sleep apnea, and…
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Dextroamphetamine (Go Pills)
Dextroamphetamine tablets issued to US military aviators to maintain wakefulness and cognitive performance during extended…
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Dim-Light Melatonin Onset (DLMO)
The time in the evening when your body begins producing the sleep hormone melatonin, measured under dim lighting conditions to…
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F
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Fatigue Risk Management System
A regulatory framework that lets aviation operators manage crew fatigue through validated fatigue models and operational data,…
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Fear Extinction
The brain’s process of learning that a previously threatening stimulus is no longer dangerous. During fear extinction, the…
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Five and Dime Watch Schedule
The US Navy’s traditional watch rotation in which sailors stand duty for 5 hours, then rest for 10 hours, cycling…
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Flight Duty Period
The total time a flight crew member is on duty for a flight, from showing up at work through landing the aircraft. Limited by…
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Glucocorticoid
A class of steroid hormones, with cortisol as the most important in humans, that regulate metabolism, immune function, and the…
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Glymphatic System
The brain’s nighttime waste-clearance plumbing. While you sleep, cerebrospinal fluid flushes through brain tissue and washes…
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H
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Heart Rate Variability
The natural variation in time between heartbeats. Higher HRV typically signals better autonomic nervous system regulation;…
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Homeostatic Sleep Drive
The growing pressure to sleep that builds while you’re awake and dissipates during sleep. Adenosine accumulation in the brain…
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HPA Axis
The Hypothalamic-Pituitary-Adrenal axis — a three-part system linking your brain (hypothalamus → pituitary gland) to your…
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Hyperarousal
A state of chronically elevated physiological and psychological arousal — including elevated heart rate, heightened threat…
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Hypervigilance
A state of persistently elevated threat-detection: the brain’s alarm system locked in the ‘on’ position, continuously scanning…
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Hypnogram
A graph showing how sleep stages change across the night. Time runs along the bottom; stages run up and down. The pattern…
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Hypoxia
Insufficient oxygen reaching the body’s tissues. In sleep medicine, repeated nighttime hypoxia from sleep apnea drives…
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I
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Image Rehearsal Therapy (IRT)
A cognitive behavioral therapy for chronic nightmares in which the patient selects a recurrent nightmare, writes a new, less…
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Imagery Rehearsal Therapy (IRT)
A structured psychological treatment for posttraumatic nightmares in which the patient consciously rewrites the nightmare…
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Insomnia
Difficulty falling asleep, staying asleep, or waking earlier than intended, with daytime consequences, occurring at least…
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L
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Light at Night
Exposure to artificial light during what should be the biological night. Suppresses melatonin, delays circadian timing, and is…
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Locus Coeruleus
A small cluster of norepinephrine-producing neurons in the brainstem that serves as the brain’s primary arousal center,…
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M
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Medical Evaluation Board (MEB)
A formal military medical review process convened when a service member’s medical condition may prevent them from meeting…
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Melanopsin (ipRGCs)
A light-sensitive pigment found in specialized retinal ganglion cells (ipRGCs) that detects light for circadian regulation,…
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Melatonin
A hormone your brain produces at night that signals it’s time to sleep. Production ramps up when it gets dark and drops off in…
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Military Sexual Trauma (MST)
Military Sexual Trauma (MST) is the VA’s term for sexual assault or repeated threatening sexual harassment experienced during…
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Military Sleep Deprivation
Military sleep deprivation refers to the systematic, often institutionally enforced restriction of sleep that characterizes US…
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Modafinil (Military Use)
A wakefulness-promoting medication used in military aviation and special operations to maintain alertness during sustained…
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Moral Injury
Psychological distress that develops after acts of commission, omission, or betrayal that violate deeply held moral values.…
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Nexus Letter
A nexus letter is a written opinion from a licensed physician or healthcare provider stating, at minimum, that it is ‘at least…
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Night Vision Goggle Use and Circadian Disruption
The circadian disruption caused by extended use of night vision goggles (NVGs), which amplify green-spectrum light and require…
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Nightmare Disorder
A sleep disorder characterized by repeated, distressing nightmares that cause significant distress or impairment,…
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No-Go Pills
Military slang for prescribed sleep aids used to ensure rest during operational sleep windows. The complement to go-pills…
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Nocturnal Blood Pressure Dipping
The normal 10-20% drop in blood pressure that occurs during sleep. Failure to dip is a cardiovascular warning sign linked to…
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Norepinephrine (NE)
Norepinephrine is a neurotransmitter and hormone released by the locus coeruleus and adrenal medulla. It drives arousal,…
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O
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Obstructive Sleep Apnea (OSA)
A condition where the throat repeatedly collapses during sleep, blocking breathing for seconds to a minute at a time, dozens…
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Orexin
A pair of neuropeptides made in the lateral hypothalamus that keep you awake and alert. Without them, you fall asleep at the…
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Paraventricular Nucleus
A small hypothalamic region that controls the body’s stress response, autonomic outflow, and the pathway from circadian clock…
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Parkinson’s Disease
A progressive movement disorder caused by loss of dopamine-producing neurons. Sleep problems often appear years before the…
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Pineal Gland
A small pea-sized gland at the center of the brain that produces melatonin — the hormone that signals nighttime to every cell…
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Polysomnography (PSG)
A comprehensive overnight sleep study that simultaneously records brain waves (EEG), eye movements, heart rhythm (ECG), muscle…
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Post-Traumatic Stress Disorder
A psychiatric condition that develops after exposure to actual or threatened death, serious injury, or sexual violence. Sleep…
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Prazosin
Prazosin is an alpha-1 adrenergic receptor antagonist originally developed as an antihypertensive. In sleep medicine, it is…
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Pre-Deployment Sleep Banking
The practice of deliberately extending sleep duration in the days or weeks before an anticipated period of sleep restriction,…
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Psychomotor Vigilance Task (PVT)
A 10-minute reaction-time test used to measure how fatigue impairs sustained attention. Participants press a button when a…
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R
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REM Sleep
A stage of sleep marked by vivid dreaming and high brain activity.
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REM Sleep Behavior Disorder (RBD)
A sleep disorder where the normal paralysis during dreaming fails, causing people to physically act out their dreams—punching,…
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Retinohypothalamic Tract
The dedicated nerve pathway from specialized retinal cells to the suprachiasmatic nucleus. It carries the light signal that…
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S
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Service Connection (VA)
Service connection is the legal determination by the VA that a veteran’s current medical condition was incurred during, caused…
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Shift Work Disorder
A circadian sleep disorder caused by working hours that conflict with the body’s internal clock. It produces insomnia during…
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Sleep Architecture
The structural organization of sleep into distinct stages (N1, N2, N3, and REM) that cycle throughout the night in a…
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Sleep Avoidance
Deliberately delaying or refusing sleep despite no external reason. In trauma survivors, often driven by fear of nightmares;…
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Sleep Debt
The accumulated difference between how much sleep you need and how much you actually get. If you need 8 hours but only sleep…
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Sleep Efficiency
The percentage of time in bed actually spent asleep — total sleep time divided by total time in bed, multiplied by 100. Normal…
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Sleep Fragmentation
Sleep that is repeatedly interrupted, so it never becomes deep and restorative for long.
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Sleep Gate
The 1-2 hour window each night when the body is biologically prepared for sleep onset. The gate opens roughly 2 hours after…
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Sleep Inertia
Sleep inertia is the grogginess, impaired performance, and disorientation that occur immediately after waking, particularly…
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Sleep Onset Latency
The time it takes to fall asleep after intending to sleep, measured from ‘lights out’ to the first epoch of sleep. Normal…
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Sleep Opportunity
The total time available for sleep, from when you go to bed to when you get out of it. This is different from how much you…
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Sleep Pressure
The biological drive to sleep that builds during wakefulness and dissipates during sleep — the body’s running tally of how…
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Sleep Restriction Therapy
The primary active component of CBT-I, in which the patient temporarily limits time in bed to match their actual average sleep…
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Sleep Spindles
Brief 11-16 Hz bursts of brain activity that fire dozens of times per night during stage 2 sleep. They help consolidate memory…
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Slow-Wave Sleep
The deepest stage of non-REM sleep (stage N3), characterized by slow, high-amplitude brain waves called delta waves. This is…
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Stimulus Control
A behavioral component of CBT-I that reassociates the bed and bedroom with sleep (and sex only), by restricting all…
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Strategic Napping
The deliberate use of short, timed sleep periods to reduce accumulated sleep debt, restore alertness, and offset circadian…
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Suprachiasmatic Nucleus (SCN)
A tiny cluster of about 20,000 nerve cells in your brain that acts as your body’s master clock, coordinating the timing of…
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Sustained Operations
Military missions that continue without scheduled rest periods, often lasting more than 24 hours. They produce predictable…
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Time Zone Transition Fatigue
The occupational fatigue of military and aviation personnel who regularly cross multiple time zones as part of their duties,…
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Total Sleep Time
The actual amount of time spent asleep during a sleep period, excluding time awake in bed. Measured by polysomnography or…
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Trauma-Associated Sleep Disorder (TASD)
A proposed sleep disorder specific to trauma survivors that combines trauma-related nightmares with physical dream enactment…
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Two-Process Model of Sleep Regulation
The dominant theory of how sleep is timed. It says two systems work together: a homeostatic pressure that builds the longer…
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W
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Wake After Sleep Onset (WASO)
The total minutes of wakefulness after initially falling asleep — a measure of sleep fragmentation and maintenance insomnia.…
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Watch Schedule (Military)
A rotating duty schedule aboard naval vessels or in military operations that divides the day into work and rest periods. The…
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Watchstanding
The naval practice of maintaining continuous, alert monitoring of a vessel’s navigation, engineering, or combat systems by…
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Z
You Are Not Alone
Sleep disorders, PTSD, and the invisible wounds of service can feel isolating. If you or someone you know is in crisis or experiencing thoughts of self-harm, help is available right now. The Veterans Crisis Line provides free, confidential support 24 hours a day, 7 days a week to veterans, service members, and their families.
If you are in crisis or experiencing thoughts of self-harm, call the Veterans Crisis Line at
