Circadian fatigue: what to know

Your circadian rhythm helps time sleep, alertness, body temperature and hormone activity. Crossing time zones, working nights, changing schedules or getting bright light at the wrong time can leave you sleepy when you need to be awake and alert when you want to sleep. Headache, poor concentration and irritability can accompany the fatigue.

Fatigue is not always circadian. Anaemia, dehydration, infection, kidney disease, coeliac disease, burnout, alcohol problems and other conditions can also reduce energy. Persistent or worsening fatigue deserves assessment rather than an assumption that the body clock is the only cause.

Choose a consistent wake time, seek outdoor light soon after waking, and keep the bedroom dark and quiet when sleeping. Shift a schedule gradually where possible, protect a wind-down period, and avoid driving when very sleepy. Regular meals, adequate fluids and gentle activity can support alertness, while late caffeine may make the next sleep period harder.

Keep a sleep and fatigue diary showing work times, naps, light exposure, caffeine, alcohol and symptoms. This can reveal patterns and helps a clinician decide whether further checks are needed.

Arrange medical review if fatigue continues despite a stable routine, interferes with work or safety, or comes with weight change, breathlessness, persistent fever, marked thirst or daytime sleepiness. Seek urgent help for chest pain, severe breathing difficulty, fainting, new confusion or sudden weakness.

Ask whether your pattern fits circadian disruption, whether medicines or an underlying condition could explain it, how to manage shift work or travel, and whether blood tests or sleep assessment would help.