The Royal College of Psychiatrists states that at any given time, one in every five people feel unusually tired and one in 10 have prolonged fatigue. In order to understand the problem, it can be helpful to be aware of the possible reasons why someone may feel this way. These fall into three main categories:

Physical causes include conditions often associated with tiredness such as pregnancy, glandular fever, anaemia, cancer and an underactive thyroid. But there are some less obvious but nonetheless common culprits, such as diabetes, autoimmune disorders and liver, heart and respiratory illnesses. Painful conditions like arthritis can also be very tiring, as can being significantly under- or overweight.

Psychological causes include depression, insomnia, anxiety and stress – whether this is negative (e.g. work or relationship issues or bereavement) or positive (e.g. getting married or moving house). It is worth noting that, contrary to popular opinion, tiredness with a psychological cause is much more common than tiredness caused by a physical problem.

Lifestyle causes can include drinking too much alcohol (particularly in the evening), suffering from disturbed sleep (most commonly because of caring for young children, shift work or sleeping during the day), too high a caffeine intake (six cups of coffee or 10 cups of tea a day can have an adverse effect), exercising excessively and not getting enough sleep.