Tiredness: What's the cause?

I have been to two different doctors in the past month complaining of feeling generally run-down. The second doctor listened to my heart and lungs, felt my belly, tested my urine but couldn't find anything wrong. Now I've begun to sweat heavily in bed. I work long days behind a desk, but in the evening I just want to lie down and sleep. Until a few months ago I was full of energy and up for anything. I am 35 years old, a non-smoker, and consider myself to be perfectly healthy.

Dr Fred Kavalier answers your health question:

GPs sometimes talk about patients who are suffering from Tatt syndrome, which stands for "tired all the time". Fatigue can be a sign of stress at work, depression and a multitude of other conditions, but the sweating at night needs to be taken seriously. Despite your recent examination, you need to have a more thorough consultation and some blood tests. Your symptoms can be the first sign of serious illnesses such as lymphoma, tuberculosis or chronic leukaemia. You may not turn out to have anything bad, but it should be investigated.

Please mail your questions for Dr Fred to health@independent.co.uk. He regrets that he is unable to respond personally to questions.