I think it was the CDR that was switched on when I first got CFS, when I was 18. I got a viral infection that lasted for weeks as I remember. I recovered to about 80% in the next couple of years, but never fully.
I think the virus might have switched on the CDR making me sick. I cleaned up my junk food diet, stopped drinking and started taking some supplements, which slowly gave me back most of my health. I had a very unhealthy lifestyle. I think the viral infection was just the straw that broke the camels back!
However, I slowly became disabled again with CFS over the next 8-10 years. So it seems the CDR can be turned on like a switch or slowly over a long period of time. They both happened to me and they both left me disabled.
My main focus now is treating the primary ongoing cause of the CDR which I believe is a leaky gut. Easier said then done though!

Although I am also treating the CDR with mito. supps, B vits. etc.
Here is a link to the web version of the paper posted above, instead of the PDF if anyone wants to take a look at it. He lists many vitamins, minerals, amino's etc. and explains how they can help reverse the CDR.
Jim