I has acute onset, combined with flu like symptoms. But I'm convinced it wasnt viral in my case. In my case I think it was a perfect storm type scenario all occurring with the months of getting CFS:- too many hours working (80+ per week), some relationship problems, some finance problems, some domestic problems with flat mates, some work problems, another unrelated health scare, lots of antibiotics, a poor diet, and big shift in training to long runs which i wasnt used to. At the time i thought I had flu, but I had no fever or raised temperature. In hindsight my gut feeling is my body had simply had enough and caved in. I think in isolation I would have coped with most of these fine, the emotional problems didnt even make me unhappy, just very angry, and for perhaps a 2-3 month period everything was just ramped up in my life, and couldnt escape it. Funny thing is I didnt even think I was stressed at the time. My response to any problem has just been to bull through it. With CFS that hasnt worked.