Adults are supposed to get seven to nine hours sleep every night, according to the NHS.

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However, many Brits miss this mark by some margin, with more than 14 per cent saying they sleep five or less hours a night, according to a Direct Line survey.

Missing out on sleep is an obvious reason for why you might be feeling tired.

It can also increase your risk of a host of conditions including high blood pressure, diabetes, obesity, depression, heart attack, and stroke.

However, feeling exhausted for long periods or even when you are sleeping right could be a sign of other illnesses.

There are five health conditions that can cause a constant state of fatigue and may mean you need to see a doctor, according to the health service.

Sleep apnoea

Feeling tired during the day because you keep waking up at night could be a sign you have sleep apnoea.

The condition causes walls of the throat to relax and narrow during sleep, interrupting normal breathing.

Symptoms include breathing stopping and starting, making gasping, snorting or choking noises and loud snoring.

During the day you might find it difficult to concentrate, have mood swings and suffer headaches when you wake up.

The NHS recommends you see a GP if you are showing any of the signs of the condition.

Iron deficiency

Low energy during the day with noticeable heart palpitations could mean you are suffering anaemia.

It is caused by having low levels of iron, which is used by the body to make red blood cells.

Iron is found in red meat, so anaemia can be more common in vegetarians and vegans, although the nutrient can also be gained from vegetables like spinach, sweet potatoes and peas.

Symptoms of iron deficiency anaemia can also include pale skin and shortness of breath.

If you have symptoms, your GP can check you for the condition with a simple blood test.

Diabetes

If you feel very tired and also have a constant thirst and need to pee, you may be suffering from diabetes.

The condition causes your blood sugar to become too high and there are two types.

Type 1 diabetes is caused by your immune system attacking the cells that produce insulin and occurs in around 10 per cent of all diabetes patients.

The more common type 2 is caused by your body having problems with the hormone insulin, either not producing enough of it or cells not reacting to it properly.

Other symptoms can include sudden weight loss, thrush and blurred vision.

You should see your GP as soon as possible if you suffer the signs, the NHS says.

Overactive thyroid

Feeling tired all the time while also struggling to stay still, feeling anxious, nervous or irritable could mean you have an overactive thyroid.

It means the small butterfly-shaped gland in the neck is producing too many hormones that affect your heart rate and body temperature.

The condition can affect anyone but is 10 times more common in women than men and usually occurs from age 20 to 40.

An overactive thyroid can also cause swelling in your neck, muscle weakness, twitching or trembling and weight loss.

If you are suffering symptoms, your GP can do a blood test to check how well your thyroid is working.

ME or chronic fatigue syndrome

Suffering extreme tiredness for more than three months is a warning sign you have ME or chronic fatigue syndrome.

Experts are not sure what exactly causes the condition but some believe it may be a long-term reaction to infections like glandular fever or pneumonia.

It can also cause problems with thinking, memory or concentration and flu-like symptoms.

They can vary so it’s important you see a GP to get a correct diagnosis, according to the NHS.

A doctor can diagnose it by ruling out other conditions.