Dr Rupal Shah, a GP in south London, says tiredness is one of the most common complaints she sees in her surgery. “I see loads and loads of patients who complain of feeling exhausted, even though they’re sleeping well. Often it’s been going on for several months.”

At any given time, one in five people feels unusually tired, and one in 10 have prolonged fatigue, according to the Royal College of Psychiatrists. Women tend to feel tired more often than men.

“It’s unusual to find anything physically wrong. Most of the time, fatigue is linked with mood and the accumulation of lots of little stresses in life,” says Dr Shah.

Dr Shah says she routinely takes a blood test from patients complaining of tiredness to rule out a medical cause, such as anaemia or an underactive thyroid gland.

“There’s more chance of a medical reason for tiredness if there are other symptoms as well, such as heavy periods, weight loss, a change in bowel habits, hair loss, extreme thirst and so on.”

If you want to work out how you became tired in the first place, it can help to think about:

parts of your life, such as work and family, that might be particularly tiring

any events that may have triggered your tiredness, such as a bereavement or relationship break-up

how your lifestyle may be making you tired

Physical causes of tiredness

There are lots of health complaints that can make you feel tired. Not just the well-recognised ones like anaemia and thyroid problems, but also more surprising ailments, such as diabetes, food intolerance and a sleeping disorder called sleep apnoea.

Read more about the medical causes of tiredness.

Being overweight or underweight can cause tiredness. That’s because your body has to work harder than normal to do everyday activities. If you’re underweight, you have less muscle strength, and you may feel tired more quickly.

Pregnancy, especially in the first 12 weeks, can also sap your energy.

Psychological causes of tiredness

Psychological tiredness is far more common than tiredness that’s caused by a physical problem.

One key reason is anxiety, which can cause insomnia and, in turn, lead to persistent fatigue. A survey by the Mental Health Foundation found that nearly a third of the population are severely sleep-deprived, often because of job and money worries. The Foundation’s report, Sleep Matters, suggests a link between insomnia and low energy levels.

The worries and strains of daily life can be exhausting – even positive events, such as moving house or getting married. Emotional shock, such as bad news, bereavement or the break-up of a relationship, can make you feel drained.

Mental health problems such as depression or anxiety can make you feel more tired. They can also prevent you from getting a proper night’s sleep.

If you think your tiredness may be rooted in low mood, try this short audio guide to dealing with your sleep problems.

Lifestyle causes of tiredness

Tiredness can often be attributed to lifestyle factors, such as drinking too much alcohol, or having a bad diet. If you drink alcohol in the evening, it tends to wake you in the middle of the night. If you drink a lot regularly, it can make you depressed and affect your sleep. “I’m always surprised to find how often patients who complain of tiredness are drinking far too much,” says Dr Shah.

If you have a disturbed sleep pattern – for instance, if you work night shifts, sleep in the day or look after young children – it can be difficult to get a good night’s sleep, and you’ll feel tired during the day.

Read more about how to change your lifestyle to boost your energy.

How to tackle tiredness

It may be common to feel tired all the time, but it isn’t normal. If you’re worried, see your doctor for advice and reassurance. “We can rule out anything serious,” says Dr Shah. “Just knowing there’s nothing wrong can be reassuring in itself.”