Sleep Better

Appendix: Sleep terms

A plain-English glossary of the terms used in this course.

How sleep works

Term	Meaning
Adenosine	A chemical that builds up in the brain while you’re awake and creates sleep pressure. Caffeine blocks its effect.
Sleep pressure	The growing drive to sleep the longer you’ve been awake. Also called sleep drive or “process S”.
Circadian rhythm	The body’s roughly 24-hour internal cycle of alertness, temperature and hormones. Also called the body clock or “process C”.
Body clock	Everyday name for the circadian system, run by a master clock in the brain’s hypothalamus (the suprachiasmatic nucleus).
Melatonin	A hormone released in darkness that signals “night” to the body. Bright light, especially blue-rich light, suppresses it.
Melanopsin	A light-sensitive pigment in special cells of the eye that report brightness to the body clock. Most sensitive to blue light, least to red.
Sleep cycle	One pass through the sleep stages, about 90 minutes. Most people have four to six a night.
N1	The lightest stage of sleep: the doze as you drift off.
N2	Light sleep, where about half the night is spent.
N3 / deep sleep / slow-wave sleep	The deepest stage, concentrated early in the night. Hardest to wake from.
REM sleep	Rapid eye movement sleep: vivid dreams, an active brain and temporarily relaxed muscles. Longest towards morning.
Sleep architecture	The pattern of stages and cycles across a night.
Sleep inertia	The grogginess just after waking, worst when woken from deep sleep.
Glymphatic system	The brain’s waste-clearing system, which studies in animals show works faster during sleep.
Chronotype	Your natural timing: lark (early), owl (late) or in between.

Measuring sleep

Term	Meaning
Total sleep time	How long you actually slept, not counting time awake in bed.
Time in bed	From getting into bed to getting up.
Sleep onset latency	How long it takes to fall asleep.
Sleep efficiency	Time asleep divided by time in bed. 85% or more is generally considered good.
Sleep window	The fixed hours you allow for sleep, used in sleep restriction therapy.
Sleep diary	A daily record of when and how well you slept. The main tool for spotting patterns and for CBT-I.
Polysomnography	The full overnight sleep study in a lab, measuring brain waves, breathing, oxygen and movement. The gold standard.
Wearable / sleep tracker	A watch or ring that estimates sleep from movement and heart rate. Good for trends and total sleep, rougher for stages.
HRV (heart rate variability)	The natural variation in time between heartbeats. Higher overnight HRV generally signals better recovery.
Resting heart rate	Your heart rate at rest, often lowest during sleep. A rise above your usual can signal poor sleep, stress, illness or alcohol.

Problems and treatments

Term	Meaning
Insomnia	Trouble falling asleep, staying asleep or waking too early that affects your day.
Chronic insomnia	Insomnia at least 3 nights a week for at least 3 months.
CBT-I	Cognitive behavioural therapy for insomnia: the recommended first treatment for chronic insomnia.
Stimulus control	A CBT-I technique to retrain the bed as a cue for sleep: bed only when sleepy, up if awake.
Sleep restriction	A CBT-I technique that limits time in bed to actual sleep time, then extends it as sleep improves.
Sleep hygiene	The everyday habits and environment that support sleep: light, caffeine, alcohol, bedroom, routine.
Sleep debt	The accumulated shortfall when you sleep less than you need.
Social jetlag	The shift in body clock caused by sleeping much later on days off than on work days.
Jet lag	Body clock out of step with local time after crossing time zones.
Obstructive sleep apnoea (OSA)	Repeated narrowing or closing of the throat during sleep, causing breathing pauses and brief awakenings.
Nocturia	Waking at night to pass urine.
Restless legs syndrome	An uncomfortable urge to move the legs, usually in the evening or at night, eased by moving.
Narcolepsy	A condition causing overwhelming daytime sleepiness and sudden sleep attacks.
Parasomnia	Unusual behaviour during sleep, such as sleepwalking, sleep talking or acting out dreams.
Orthosomnia	Worry and poorer sleep caused by trying to perfect sleep-tracker scores.
Hypnotic	A medicine that causes sleep, such as a sleeping tablet.
Benzodiazepine	A class of sedative medicines, including temazepam, used short-term for sleep. Risk of tolerance and dependence.
Z-drug	Sleeping tablets such as zolpidem and zopiclone that act similarly to benzodiazepines.
Tolerance	Needing a larger dose of a medicine for the same effect.
Rebound insomnia	Temporarily worse sleep after stopping a sleeping tablet, especially if stopped suddenly.
Taper	Reducing a medicine’s dose gradually rather than stopping all at once.

Lifestyle

Term	Meaning
Power nap	A short nap of 10 to 20 minutes that refreshes without deep sleep.
Cognitive shuffling	Picturing a series of random, unrelated objects to imitate the loose thinking of drifting off. Also called serial diverse imagining.
Imagery distraction	Imagining a pleasant, detailed scene to crowd out worries at bedtime.
Paradoxical intention	Gently trying to stay awake in bed, which removes the pressure of trying to sleep.
NSDR	Non-sleep deep rest: guided deep relaxation, similar to yoga nidra or a body scan.
Cyclic sighing	A double in-breath through the nose followed by a long, slow out-breath. Also called the physiological sigh.
Elemental magnesium	The amount of actual magnesium in a supplement, as opposed to the weight of the whole compound.
AUST L	Label code for “listed” complementary medicines in Australia, checked for safety and quality but not for whether they work.
Wind-down	A calm routine in the hour or two before bed.
10-3-2-1-0	A countdown rule: no caffeine 10 hours before bed, no food or alcohol 3 hours before, no work 2 hours before, no screens 1 hour before, no snooze.
Psychological detachment	Genuinely switching off from work in your own time.
Blue Zones	Regions reported to have unusually many long-lived people, and the lifestyle habits (“Power 9”) drawn from them.
Ikigai	Okinawan word for your reason for getting up in the morning.
Downshift	Blue Zones habit of a daily routine to shed stress.

This course is general information, not medical advice. If you have ongoing sleep problems, loud snoring with pauses or gasping, or sleepiness that affects driving or work, see your doctor. In Australia, if you are struggling or feel unsafe, call Lifeline on 13 11 14.