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Diagnosing Non-24

Non-24 is diagnosed by a clinician — usually a sleep specialist — from a long, continuous record of your sleep timing that shows the tell-tale daily drift, together with tests that rule out other explanations. This page explains what that process usually involves so you know what to expect and how to prepare.

Not a diagnostic tool

This page is a community overview, not medical advice, and Zeitdex cannot diagnose you. A sleep diary can suggest a pattern, but a diagnosis — and access to treatment — needs a qualified clinician. If you suspect a circadian rhythm disorder, see how to find a specialist.

Why Non-24 is hard to diagnose

The hallmark of Non-24 is drift: sleep onset and wake time move progressively later (occasionally earlier) day after day, cycling around the clock over weeks. A single night — or even a single week — can look completely normal, because at any given moment your timing may happen to line up with the day. The pattern only becomes obvious over a long record.

It is also clearest when you are free-running — living by your own body clock with no fixed obligations pulling you onto a schedule. Work, school, alarms, and social commitments mask the underlying rhythm, so the same tests can be inconclusive if you are forced onto a fixed timetable while they are run.

Keep a long diary before your appointment

Most clinics ask for at least two weeks of sleep records before an appointment, and a longer record is better for showing drift. The Zeitlog tracker is built for exactly this — it charts sleep over time so a free-running rhythm shows up as a diagonal band. See Recognising your pattern for what to look for.

How it's assessed

  •   Sleep diary / actogram

    A self-kept log of when you sleep and wake, plotted over many days. The clearest evidence of Non-24 is a chart showing timing marching steadily later. This is the foundation of the assessment.

  •   Actigraphy

    A wrist-worn movement sensor worn continuously for weeks gives an objective estimate of your sleep-wake timing, to corroborate (or replace) a hand-kept diary.

  •   Melatonin timing (DLMO)

    Dim-light melatonin onset is the evening time, measured from saliva or blood under dim light, when melatonin secretion begins — a marker of your internal clock's phase. Sampled on different days, it can show the clock drifting. Mostly available in specialist or research settings.

  •   Sleep study (PSG + MSLT)

    An overnight polysomnogram and daytime nap test don't diagnose Non-24 directly. They're used to find or rule out other conditions — like sleep apnea or narcolepsy — that can affect sleep.

Ruling out look-alikes

Part of the work-up is distinguishing Non-24 from conditions that can resemble it:

  • Delayed sleep-wake phase disorder (DSPD). A late but stable schedule, rather than one that keeps drifting. DSPD can sometimes progress into Non-24. (See the Overview for how the circadian disorders relate.)
  • Irregular sleep-wake rhythm. Sleep broken into several episodes across the day without a clear marching pattern.
  • Shift work and behavioural causes. An irregular environment or schedule can mimic a circadian disorder; a free-running record helps separate these.
  • Comorbid sleep disorders. Conditions like sleep apnea don't cause Non-24, but treating them improves sleep quality — and untreated, they can make any entrainment attempt harder. It's worth checking for them either way.

Rule out carbon monoxide

Rare, but easy to exclude and dangerous enough to take seriously: a boiler leaking carbon monoxide can disturb sleep. A carbon monoxide detector settles the question quickly, and is a household necessity regardless.

Blind and sighted Non-24

Non-24 is most common in people who are totally blind — without light perception, the eye cannot deliver the light signal that keeps the clock set to 24 hours, so more than half of totally blind people experience it. It also occurs in sighted people, where the causes are different and often less well understood. The two are distinct situations, and research increasingly treats them separately.

Why a diagnosis is worth pursuing

Getting a formal diagnosis can be slow and frustrating, but it matters:

  • It opens the door to treatment — including the only FDA-approved medication for Non-24, tasimelteon.
  • It supports requests for accommodations at work or school.
  • Every diagnosis enlarges a very small known population, which is what drives more research and better care for everyone who comes after.

Find a specialist   Start a sleep diary

See also

Contributions welcome

Clinician-reviewed detail, links to diagnostic criteria, and lived-experience notes on getting diagnosed would all improve this page — contribute here.