I trained as a cyclist very intensively, for 20 hours a week for six months. But because I'm not a lifelong athlete, I didn't have the physical endurance to cope with that regimen, and my immune system broke down. Within the space of two weeks, I went from being really very fit to almost being unable to get out of bed. No one knew what was wrong with me. I had lots of tests before they found out that my white blood cell count had gone down to a dangerously low level. For a while, they thought I had a form of leukemia. It was very scary, and I got depressed.