Should I try to run a marathon with fibromyalgia and a chronic lung condition? ?

I was recently diagnosed with fibromyalgia. After three visits, the doc told me I should be doing extreme exercise such as running a marathon or doing bicycle races. I also have a lung condition that my other doc says will be emphysema in a short period of time. The FM doc knows this. Am I the only one that thinks it might be a bit unsafe for me to attempt something that extreme?