Sleep, Actually
Common sleep vocabulary
The words that appear in letters, reports, and appointments — collected in one plain-English list.
Plain-Language NAP ExplanationSources cited. No clinician review claimed.Last reviewed August 8, 2026
Clinic letters assume a vocabulary nobody hands you. This page collects the recurring words in plain English so a report is at least readable.
A definition is not an interpretation. Knowing what a term means does not tell you what your result means — that stays with your clinician.
Definitions on this page
- Actigraphy
- Estimating sleep and wake from movement recorded by a worn device.
- Apnoea
- A pause in breathing during sleep; assessed in an overnight study.
- Arousal
- A brief shift toward lighter sleep or wakefulness, often unremembered.
- Circadian rhythm
- The roughly 24-hour internal cycle influencing sleep and wake timing.
- Hypersomnia
- An umbrella term for excessive sleepiness or sleep amount.
- Hypocretin (orexin)
- A brain signalling chemical involved in staying awake.
- Sleep architecture
- The overall pattern of stages and cycles across a night.
- Sleep hygiene
- General habits around sleep timing and environment. Not a treatment for narcolepsy.
- Sleep onset
- The moment of falling asleep, as recorded in a study.
- Total sleep time
- The amount of time actually spent asleep during a recording.
- Wake after sleep onset (WASO)
- Time spent awake after first falling asleep.
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