I suspect this may true of more of us than we currently realize. We may have had ME for years (maybe all our lives), but it wasn't recognized until something sufficiently damaging knocked us over the edge into disability.
I often think about the history of HIV and some of the similarities to our history. For years the thinking was that the disease was AIDS, which was recognized when patients developed serious infections from pathogens ordinarily controlled by the human immune system. All AIDS patients were very, very ill people. Once they discovered the cause, HIV, they realized that the majority of patients with the disease were
not those severe AIDS patients, but people who appear healthy or nearly so. The AIDS patients were just the easily-identified severe tip of the iceberg.
The same could be true for us. What we see as "real ME" with PEM, neuroimmune manifestations, and disability (50% reduction in activity level) may be only the severe tip of the iceberg. The illness itself may exist in people who currently don't have the symptom set we think of as ME. They may be walking timebombs, just waiting to encounter the wrong trigger -- a pathogen, a vaccine, who knows? -- that sets off the cascade that spirals down into ME. Or maybe it's just a matter of time for some people as their body systems degrade slowly from the disease without the need for the straw-that-broke-the-camel's-back single pathogen.
...
Of course, I could be completely wrong.
This is just one of a number of my random speculations about ME.