I understand acute onset. I was at work, perfectly well one day over 20 years ago about to go into a meeting. Then suddenly, really suddenly, I can time it within five minutes, I told my colleagues I was feeling so bad that I had to go home. It was pain, fog, exhaustion. All at once and sudden. At first I thought I had the flu, maybe hepatitis without jaundice.....I was worked up for everything. Every test, except some minor immune dysfunctions that were not specific came back negative and still are..... To make a long story short, the flu didn't go away for years. Obviously it is a diagnosis in retrospect. You dont diagnosis CFS in anyone at first onset. It is a diagnosis in retropect for everyone since there are so many diseases that have to be ruled out.
For the past years it has come and gone. It has returned in the past few months, waxing and waning at its own pleasure....
So I know acute onset of our thing. It seems that it doesn't happen to everyone here...However, if it happened to you, you know. I have discussed this before and there seems to be a number of threads here with people who have had the exact same experience. If you had acute onset on CFS you know. Again, while everyone's case didnt start this way, it is a hallmark for some of us.
and PS...not only viral illness strike suddenly....there are many disease systems that can be acutely affected, neurological, hormonal, stress, muscular skeletal, etc etc...