I've had the disease for 17 years now, sudden viral onset in teenage years. It used to be mild, but over the years it progressed. My nr 1. initial symptom was drastically reduced stamina. I didn't have PEM at the time so I was able to exert myself. Before the illness I used to enjoy jogging, mostly just for fun, when going from A to B I used to jog instead of walking, because I enjoyed it. I could jog continously for 15+ minutes without feeling worn out or tired. Immediately after it started, my stamina was reduced drastically. I could only jog for 1 to 2 minutes before feeling completely out of breath and destroyed. This has persisted until now. I tried to build up my stamina, by running every day. After a several weeks of doing this, the improvement in stamina was negligable so I stopped. I've also had an exercise test confirming the stamina reduction. I was in the bottom percentiles for my age group, despite being at a low body fat and having a low weight. These days I no longer try this, due to the fear of PEM. But still, this is the nr 1 thing that objectively indicates that something is wrong. If tomorrow I could magically run 10+ minutes without feeling dead, then I know I have recovered. So I wonder, is this true for everyone? Do some people have the capability to jog / run for extended periods, but choose not to, due to PEM or other reasons? Or are there sufferers who do not have reduced stamina, but still have other fatigue related symptoms?