Reference

Sleep glossary

The terms that come up when you start reading about why mornings are hard — defined plainly, with an honest note on where the popular version of the science overstates things.

Chronotype: Chronotype is an individual’s natural preference for when to sleep and be active. It is largely genetic, shifts with age, and is commonly described on a spectrum from early types who wake naturally at dawn to late types who are most alert in the evening.
Circadian rhythm: The circadian rhythm is the roughly twenty-four-hour internal cycle that governs sleep timing, alertness, body temperature and hormone release. It is set primarily by light exposure, which is why morning daylight advances it and late-night screens delay it.
Dysania: Dysania describes extreme difficulty getting out of bed in the morning, beyond ordinary reluctance. It is not a recognised clinical diagnosis, which matters: it is generally a symptom of an underlying cause such as depression, sleep apnoea, chronic fatigue or insufficient sleep.
Habituation: Habituation is the process by which the brain learns to stop responding to a repeated stimulus that carries no consequence. In the context of alarms, it is why a tone that reliably woke you in week one stops working by week four, regardless of how loud it is.
Mission alarm clock: A mission alarm clock is an alarm that cannot be dismissed with a single tap. It continues sounding until the user completes a defined task — solving arithmetic, walking a set number of steps, scanning a barcode, or photographing a specified object — which serves as evidence the user is genuinely awake.
REM sleep: REM sleep is the stage of sleep characterised by rapid eye movement, heightened brain activity resembling wakefulness, and temporary muscle paralysis. Most vivid dreaming occurs during REM, and it is associated with memory consolidation and emotional processing.
Sleep cycle: A sleep cycle is one complete pass through the stages of sleep, from light sleep into deep sleep and then into REM. A cycle lasts roughly ninety minutes on average, and most people complete four to six of them per night, with cycle composition shifting as the night progresses.
Sleep debt: Sleep debt is the cumulative difference between the sleep you need and the sleep you actually get. It builds across consecutive short nights and produces measurable declines in alertness and performance that people are typically poor at self-assessing.
Sleep drunkenness: Sleep drunkenness, clinically called confusional arousal, is a state of confusion and disorientation on waking in which a person may speak, act or respond without being properly conscious and typically without remembering it afterwards.
Sleep inertia: Sleep inertia is the period of impaired alertness and performance immediately after waking. It typically lasts fifteen to thirty minutes but can extend to an hour or more, and during it reaction time, decision-making and memory formation are all measurably worse than normal.
Snooze: Snooze is an alarm function that silences the alarm temporarily and repeats it after a short interval, most commonly nine minutes. It was introduced as a mechanical convenience rather than designed around sleep physiology, and repeated use tends to leave people less alert, not more.
Social jetlag: Social jetlag is the mismatch between your body clock and your social schedule, measured as the difference between your sleep timing on work days and free days. A two-hour difference produces effects comparable to travelling across two time zones every week.

Why these definitions are worded carefully

Sleep is a field where popular summaries drift a long way from the research. The ninety-minute cycle rule is real physiology stated with false precision. Chronotype quizzes sort people into four animals when the underlying measure is continuous. Dysania is widely written about as though it were a diagnosis, when treating it as one is actively unhelpful.

Each entry here says what the term means, and where the common version overstates the case, it says that too. Related reading lives in the blog, and the practical side is in the help centre.

Nothing here is medical advice. If mornings are consistently impossible and you are getting enough sleep, that is worth raising with a doctor rather than solving with an alarm.

Set one alarm you actually have to earn.

Pick a mission tonight. Tomorrow morning it will not let you dismiss it half asleep — and it will still let you out if you genuinely need to be somewhere.

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