About two years ago, Mark Schott, 40, was working 14-hour days in a Singapore corporate banking environment when he caught a flu that persisted longer than normal.
Three or four weeks after its onset, a doctor told him it was a post-viral infection, which lasts about six months. For Schott, sore throats, headaches, post-exercise malaise and muscle weakness continued. He took further tests and was diagnosed with chronic fatigue syndrome (CFS).
With CFS, he says, 'you know you've got it, but it's a disease of exclusion as the symptoms can be similar to other [conditions]'.
Once doctors rule out other diseases and determine that the patient's symptoms match the criteria, they can make the diagnosis.
Schott says he is typical of many CFS sufferers - a type-A, high achieving personality who was in a stressful job and overexerted himself during exercise.
'It's the overstretching of the immune system,' he says.