Non-24-Hour Sleep-Wake Disorder¶

Non-24 is a circadian rhythm sleep-wake disorder in which a person's internal clock is not entrained to the 24-hour day. The sleep-wake cycle runs longer (or, rarely, shorter) than 24 hours, so sleep timing drifts a little each day — usually later — cycling all the way around the clock over weeks.

It is common in people who are totally blind (with no light perception, the strongest zeitgeber cannot entrain the clock), and it also occurs in sighted people.

Not medical advice

Diagnosis and treatment of Non-24 belong with a qualified clinician. This page is a community overview, not a substitute for medical care.

In this section¶

Diagnosis

How clinicians identify Non-24, and how to prepare.

Diagnosing Non-24
Treatment

Light, dark, melatonin, medication — and a realistic view.

Treatment & management
Research

Mechanisms, measurement, and where the science is heading.

Research & outlook
Recognising your pattern

What the drift looks like on a chart, and living with it.

Recognising your pattern

Common features¶

Sleep onset and wake time that shift progressively later (or earlier) over days to weeks.
Alternating "good" and "bad" stretches as the rhythm cycles in and out of phase with the desired schedule — periods of daytime sleepiness and night-time wakefulness in between.
Difficulty holding a fixed social, school, or work schedule.

Long-period and short-period Non-24 (delayed vs advanced)¶

Non-24 comes in two directions, set by whether the clock's natural period is longer or shorter than 24 hours:

Delayed (long-period) Non-24 is by far the usual form. The intrinsic period is longer than 24 hours, so each cycle the body runs a little long and sleep begins later than the day before. This direction dominates partly because the average human clock already runs a touch over 24 hours, and light and modern habits tend to push it later still.
Advanced (short-period) Non-24 is the rare mirror image. The intrinsic period is shorter than 24 hours, so sleep creeps earlier each day. It is documented, but much less common.

The further the period sits from 24 hours, the faster the drift: a ~25-hour clock moves roughly an hour later each day; a ~23-hour clock, roughly an hour earlier.

At the extreme, a very short or very erratic period starts to blur toward irregular sleep-wake rhythm disorder — the difference being that Non-24 keeps a strong, predictable march, whereas ISWRD has no coherent pattern to follow.

A critical note — short cycles need hard proof

Unusually short free-running periods are rarely documented and easy to misjudge from a glance at a messy schedule. Precisely because they're so uncommon, a claim of a very short cycle really wants objective backing — extended actigraphy, and melatonin-timing (DLMO) testing where it's available — before being taken at face value.

Seeing the drift¶

Because the hallmark is drift, a long, continuous record of sleep timing is the clearest way to see the pattern. The Zeitlog tracker charts sleep over time, so a free-running rhythm shows up as a diagonal band marching across the chart.

Track your sleep with Zeitlog Find a specialist