How this course was made
Sleep, Decoded is an original course. Every sentence was written for this site, and every fact is checked against open, citable sources: the US National Heart, Lung, and Blood Institute (NHLBI), the US National Institute of Neurological Disorders and Stroke (NINDS), the Centers for Disease Control and Prevention (CDC), the American Academy of Sleep Medicine (AASM), the NHS, the European Food Safety Authority (EFSA), the Sleep Foundation, and peer-reviewed studies listed on PubMed. Each page lists its own sources at the bottom. Before a module is published, a separate fact-check compares every claim with the source it cites, and the corrections are made. Where a number is our own estimate or suggestion, the page says so.
Who writes it
The course is written by an online teacher who has taught IT to hundreds of thousands of learners, as a careful reader of the research, not as a doctor.
Education, not medical advice
This course is educational content. It has not been reviewed by a doctor or other clinician, and it is not medical advice. It cannot diagnose, treat or rule out any condition, and it does not replace a consultation. If you have symptoms, or you are worried about your sleep or your health, see your GP or another qualified health professional. The red "See a doctor if..." boxes list signs that need a professional, not a course. In an emergency call 999 (UK) or your local emergency number.
We are looking for a volunteer sleep-health reviewer (a clinician, sleep scientist or sleep technologist) to read the modules and tell us what to fix. If that is you, please get in touch.
Your data
There are no trackers and no accounts. Your progress, quiz scores, flashcards and sleep diary are saved only in this browser (localStorage). Nothing is sent anywhere. Clearing your browser data deletes them; use the diary's Export button to keep a copy. Reset my progress
Glossary
- Anchor time
- One wake-up time that you keep on all seven days, within about 30 minutes.
- Caffeine half-life
- The time it takes the body to clear half of the caffeine taken in; about 4 hours on average in healthy adults, from 2 to 8 hours between people.
- Chronotype
- Where your body clock sits on the range from early (morning types) to late (evening types). It shifts with age.
- Deep sleep (N3)
- The deepest stage of non-REM sleep, in longer periods during the first half of the night.
- Estimated sleep
- Time from lights out to your final wake-up, minus the time it took to fall asleep and the time you were awake in the night.
- Lapse
- In a reaction test, a response that is very slow (500 ms or more), a sensitive sign of sleep loss.
- Lights-out window
- The range of times to switch off the light so that you get your recommended sleep before your anchor time.
- REM sleep
- Rapid eye movement sleep, when most dreaming happens; REM periods get longer later in the night.
- Sleep debt
- The gap between the sleep you need and the sleep you get, added up over several nights.
- Sleep efficiency
- Estimated sleep divided by time in bed, as a percentage. 85% or more is a sign of good-quality sleep.
- Sleep latency
- The minutes between starting to try to sleep and actually dropping off. Within 30 minutes is a sign of good sleep.
- Sleep regularity
- How similar your sleep and wake times are from one day to the next.
- Time in bed
- From getting into bed to getting out of bed in the morning.
- Wake after sleep onset
- The total time you are awake in the night after first falling asleep.
- Wind-down
- A calm, dim, screen-light period before lights out that tells your evening it is landing.
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Module 2 opens on Tuesday 6 October. One short email when each module opens, with the link. No spam; unsubscribe with one click.