The main symptoms include some or all of the following: profound, persistent and unexplained physical and mental fatigue, which reduces activity levels; malaise or fatigue after exertion; loss of mental and physical stamina; problems with sleep, including disturbances in rhythm; pain; a variety of neurological and cognitive manifestations, like memory loss; muscle weakness; autonomic nervous system problems (such as bladder dysfunction or heart palpitations); lightheadedness; abnormal body temperature; intolerance of heat and cold; tender lymph nodes; recurrent flu-like symptoms; and sensitivities to chemicals, food or medication. Several researchers believe that ME is a new variety of polio.

What causes it? No one is sure, but a number of triggers appears to set it off, including:

* a wide range of viral infections. This has been confirmed by lab tests showing that, in half of patients, the 2-5A synthetase/ribonuclease L (Rnase) pathway is not functioning properly, as seen with viral disorders. These cellular fragments wreak havoc inside cells, and can also block thyroid receptors. Despite normal test results on routine screening, thyroid cells may not be functioning.

* one or more environmental, biological or chemical triggers. These may be vaccinations, anaesthetics, exposures to environmental pollutants, chemicals or heavy metals, a physical trauma such as a car accident, a fall or surgery or, in rare cases, a blood transfusion.

* stress. MRI (magnetic resonance imaging) scans show areas of ‘high signal’ in the white matter of the central nervous system, demonstrating a pathology of the CNS and immune system not unlike that seen in patients with AIDS (Am J Med, 2000; 108: 99-105).

What doctors tell you According to the UK Working Group on CFS/ME, set up to compile guidelines on the appropriate management and treatment of patients with CFS/ME, graded exercise and cognitive behavioural therapy (CBT) are the main treatments, plus antidepressants for those with depression. This approach underscores the medical profession’s view that this illness is largely in the sufferer’s head.

However, in four independent long-term surveys of ME patients, CBT was the least effective of seven strategies, while graded exercise therapy was clearly the most harmful. Only 24 per cent of patients improved with CBT. As for graded exercise, while 36 per cent said it helped, 48 per cent - or nearly half - said it made things worse.

Lynne McTaggart