If you're almost too exhausted to make it to your doctor for a check-up, be consoled: at least you're not alone. More people are tired today than ever before. On any day, one in five of us is feeling unusually fatigued, while one in 10 has persistent low energy, sufficient to undermine quality of life and day-to-day functioning.

Yet being tired all the time has been adopted as a bitter shorthand by Britain's doctors, who use the term TATT to describe the condition that they most dread walking through their consulting-room door. "Unfortunately, nine times out of 10 there's absolutely nothing we can do about it beyond ordering a batch of blood tests to eliminate the usual suspects," says Jarvis, a spokesperson for the Royal College of General Practitioners.

The vast majority of weary people suffer because of the way they choose to live, says Professor Fred Zijlstra of Surrey University. "People work ever-longer hours and then take files home or check their e-mails in the evening. New technology means they're on call 24/7. With double burden of being a working parent, there's a constant feeling of never getting things finished. It's this that can be so tiring."

Even so, fatigue is a symptom in a wide range of physical and psychological problems. If exhaustion is now a way of life, you could be one of the "lucky" ones with a "real", or at least treatable, condition. If not, it may be time to ask yourself some difficult questions.

ANAEMIA

Unusual tiredness is the main symptom of anaemia, a group of disorders in which insufficient red blood cells are produced to carry adequate supplies of oxygen throughout the body.

The most common type is iron deficiency anaemia, normally the result of losing blood faster than the body can make it. Around one in seven menstruating women suffers iron deficiency anaemia. It is also common during pregnancy when there is extra demand for iron.

Two other types are: vitamin B12 deficiency anaemia, which mostly affects vegetarians and vegans (B12 is only found in animal fats, meat, fish, eggs and milk); and folic acid deficiency anaemia, which occurs in pregnancy and as a result of high alcohol consumption or a poor diet, particularly in the elderly.

What to do

A blood test can diagnose anaemia, and doctors will normally recommend supplements along with dietary advice. If your blood count is at the low end of normal, but not anaemic, boosting your iron intake could make you feel better.

CHRONIC FATIGUE SYNDROME

Overwhelming exhaustion, made worse by activity and not helped by rest, could be CFS (or ME, myalgic encephalomyelitis). One in 100 people, usually in their twenties or thirties, is affected, with three times as many women sufferers as men. CFS appears to be triggered by an infection, even a minor one. It can be worsened by stress. Symptoms include muscle pain, sore throat, an inability to start or sustain activity, and finding that any increase in activity requires a prolonged recovery time.

What to do

Take as much information about your symptoms to your GP as possible. Diagnosis is tricky, and frequently involves excluding other conditions. Training in the form of graded exercise can help mild CFS. Cognitive behavioural therapy, along with a supervised lifestyle management programme, is effective in severe cases.

COELIAC DISEASE

Extreme fatigue, with bowel symptoms such as diarrhoea and bloating, can indicate a flare-up of this lifelong inflammatory condition of the small gut in response to gluten, a substance found in wheat, barley and rye. Most commonly diagnosed in people aged 30 to 45, it can come out of the blue or occur in people with a history of stomach upsets. As many as one in 100 people are thought to be affected, and as many as nine out of 10 remain undiagnosed, on some estimates.

What to do

A blood test can pick up antibodies, and the diagnosis can be confirmed by an investigation of the lining of the small bowel, normally carried out at the endoscopy unit of the local hospital. A gluten-free diet can bring real improvement in less than a week.

DEPRESSION

Severe tiredness and loss of energy that persists for most of the day, nearly every day, for more than two weeks is one of the clearest signals of clinical depression. This is suffered by up to one in 10 of the population at any one time. A GP will suspect depression when fatigue is experienced with symptoms such as loss of confidence; inability to enjoy things that are usually pleasurable; a desire to avoid people, including friends; irritability; and feeling like a "waste of space".

What to do

Consult your GP with a list of symptoms and work with him or her to decide the best treatment. This can include psychotherapy or counselling, along with medication.

TYPE 2 DIABETES

Extreme tiredness that develops slowly, with constant thirst, a need to urinate and episodes of thrush, could be type 2 diabetes. People with the disease have problems converting food into energy because the insulin, a hormone that muscle, liver and fat cells use for this, becomes ineffective, often due to obesity. While these cells are starved of energy, blood glucose levels remain high, eventually damaging nerves and blood vessels and leading to serious complications. Type 2 diabetes usually occurs in people over 40, although children as young as seven have been diagnosed. It is three times more common in Asians and West Indians.

What to do

A simple blood test will diagnose the disease and, if picked up at an early stage, changes such as weight loss, a healthy diet and exercise can prevent further deterioration.

GLANDULAR FEVER

Severe fatigue, accompanied by feverish symptoms such aching muscles, loss of appetite and swollen lymph glands in the groin, suggests the "kissing disease". The infection is most common in the teens and early twenties; by their late twenties, most people have developed immunity to the Epstein-Barr virus, which is spread in saliva via kisses, coughs or sneezes. The tiredness frequently persists for weeks or even months after the other symptoms have disappeared.

What to do

Diagnosis by symptoms can be confirmed by a blood test. Antibiotics will not help; rest is the best treatment.

LYME DISEASE

Flu-like symptoms including tiredness could be a sign of this relatively rare tick-borne infection, which can affect walkers and cyclists who fail to tuck their trousers into socks in long grass and heathland in parts of UK.

What to do

Ideally, take the tick with its identifiable bite-mark and surrounding rash to your GP. Otherwise, diagnosis is by exclusion or by a blood test around eight weeks after infection, which can be quickly cleared up with antibiotics.

SLEEP APNOEA

Severe daytime sleepiness is the most obvious symptom of sleep apnoea, where sleep is disrupted by snoring. The disorder, which actually halts breathing, sometimes hundreds of times a night, causes a brief awakening each time as the body senses what is happening and acts to prevent suffocation.

What to do

Diagnosis requires an overnight stay in hospital, although a home test is being developed. Wearing a gumshield and avoiding alcohol after 6pm can reduce snoring. Severe cases are best treated with a pump that blows air gently through the nose. It's cum- bersome, but most sufferers decide to use the machine at home every night, says the Sleep Apnoea Trust.

UNDERACTIVE THYROID (HYPOTHYROIDISM)

Tiredness and excess sleep, with symptoms including constipation, sensitivity to cold and weight gain, may be a sign of an underactive thyroid. This disorder, which is caused by the body failing to produce sufficient thyroxine hormone, thereby slowing the metabolism, is most common in older people, affecting one in 50 women and one in 1,000 men at some time in their lives.

What to do

A risk of developing the condition can be detected with a blood test to measure TSH (thyroid stimulating hormone), which is raised when the thyroid gland is not producing sufficient thyroid hormone. A further test can then measure T4, the actual level of thyroxine. A condition known as sub-clinical hypothyroidism exists when levels of TSH are raised but thyroxine levels are normal. Some doctors decide to offer thyroxine treatment to see if it works: others prefer to wait and see whether the metabolism continues to slow.

Is your life too tiring?

Do you demand too much of yourself?

If yes: try to manage stress; learn to say no; set priorities; pace yourself. Take time each day to simply relax, perhaps using a tape or relaxation class. Consider whether there is a good balance of work and play in your life and what you can do about it. If necessary, you may want to reconsider what you want from life.

Have you been affected recently by a stressful event?

If yes: Be realistic, and be kind to yourself. Events such as moving house, having a baby, starting a new job, being bereaved or ending an important relationship can be exhausting, especially when you feel you have no control over what's happening. Don't expect to be back to your normal self overnight. Remember; all progress is good, however small or unimportant it may seem to you at the time.

Is regular exercise part of your daily life?

If no: Begin to change that. If you are unfit, start with 10 minutes of moderate physical activity each day and build up to at least 30 minutes. "It may seem counter-intuitive, but aerobic exercise is an excellent way to counter fatigue," says Dr Sarah Jarvis.

Is your diet healthy?

If no: try to begin the day with an energy-packed, low-fat, high-fibre breakfast. Reduce the amount of high-fat and high-sugar foods, which will to make you feel sluggish later on. If you are underweight, gradually increase your portion sizes and calorie intake. If you are overweight, focus on eating less (but don't crash-diet) and being more physically active. There's no good evidence that vitamins, minerals, stimulants or fortified wine will help to combat tiredness.

Are you drinking too much?

If yes: cut down on the booze. It acts as a sedative, and even small amounts can make you tired for hours.

Are you sleeping well?

If no: practice good sleep habits. Avoid eating, reading or watching television while in bed. Keep your bedroom cool, dark and quiet, and set the alarm to get up at the same time each day - a routine will help you to establish a regular schedule. Staying in bed all day will not help.