Free-running circadian rhythm (non-24-hour sleep-wake disorder): symptoms and treatment

Sleep is controlled mainly by two things: sleep pressure, which builds the longer you are awake, and the body clock, or circadian rhythm. The Sleep Charity describes the body clock as following a 24-hour cycle that helps control when you feel awake and sleepy, as well as appetite and body temperature, and says it responds to changes around you, especially light and dark.

In most people the clock is nudged each day by light so that it stays in step with the 24-hour day. A UK NHS integrated care board referral pathway (Bristol, North Somerset and South Gloucestershire) describes issues with the intrinsic body clock or the external cues that synchronise it as the basis of circadian rhythm sleep disorders. In non-24-hour sleep-wake disorder, the part of the brain that controls the clock, the suprachiasmatic nucleus, does not entrain to the 24-hour day.

The result is a rhythm that "free-runs". Sleep length and wake length are regular, but because the internal rhythm is longer than 24 hours, the pathway says each day the sleep-wake cycle is delayed by at least 2 hours. Over days to weeks the person drifts around the clock, with a period where sleep fits normal night-time hours, followed by days where they are sleepy at midday and awake at night.

The pathway says non-24-hour disorder is seen most commonly in blind people. This fits with the Sleep Charity's explanation that the body clock relies on light cues to stay on track: without light reaching the clock, the signal that resets it each day is missing.

The pathway's wording is "most commonly", so it is not limited to people who are blind. It is different from delayed sleep phase, which the Sleep Charity describes as falling asleep much later than most people, often two or more hours after a typical bedtime, and struggling to wake in the morning. In delayed sleep phase the timing is consistently late, whereas in a free-running rhythm the timing keeps moving.

The symptoms are not constant; they follow the drift of the clock. The Sleep Charity notes that when body clocks get out of sync, sleep, appetite, mood and focus can all suffer. In practice people report the following.

• Difficulty falling asleep at the conventional bedtime for days at a time, then a period when it feels easy.

• Excessive sleepiness during the day when the body clock puts sleep at the wrong time.

• Waking at progressively later times, with a repeating cycle that can take weeks.

• Periodic stretches in which sleep is at night-time and symptoms ease, which can make the problem seem to come and go.

• Effects on work, study, social life, mood and concentration from repeated sleep deprivation.

The pathway says there are no specific criteria for referral besides a reasonable suspicion of the disorder and that it still interferes with daily function and does not resolve following general advice, sleep hygiene and self-help managed in primary care. It also advises that the NHS sleep clinic it describes does not take referrals for insomnia or sleep-related breathing disorders, which are directed elsewhere.

A specialist sleep clinic can offer assessment by a sleep specialist and sleep investigations such as actigraphy, a wrist-worn movement monitor, where indicated, which can show the pattern of rest and activity over weeks. The Sleep Charity offers a sleep diary tool, and a diary kept over several weeks is a simple way to show whether sleep keeps moving later. Clinics differ in what they provide, and the pathway shows that referral routes depend on the local area.

The pathway states that treatment consists of re-synchronising sleep and wake periods by medications and external stimuli. It describes several approaches and is candid about the strength of evidence.

The Sleep Charity's general advice for strengthening the body clock is to keep a regular sleep routine and wake at the same time each morning, even at weekends, to get morning light, such as a short walk outside, to reduce bright light in the evening, and to limit screens for at least an hour before bed because the light can suppress melatonin.

The NHS insomnia advice is similar: getting up at the same time every day, relaxing before bed and keeping the bedroom dark and quiet. These measures are unlikely to fully correct a free-running rhythm on their own, but they form the foundation of any treatment and are what the pathway expects to be tried in primary care first.

Because the condition arises from how the body clock is regulated, it is usually long-term, and management focuses on keeping the clock aligned and reducing the impact of sleep loss. See a GP if sleep problems are affecting your daily life, if you have had trouble sleeping for months, or if self-help has not worked, as the NHS advises for insomnia. Make a note of when you sleep and wake for a few weeks to show the pattern.

Drowsiness at the wheel is dangerous. The NHS advises not driving when you feel sleepy. If low mood or worry comes with the sleep problem and you cannot cope, tell your GP or use NHS 111.