Often the question is asked, why has the CFIDS epidemic started? My personal view is below.
A New Infection..
An infection triggering coagulation is normal -- we get headaches, tiredness etc from lots of illnesses. So an appropriate novel infection spreading rapidly is not unusual (the incline village outbreak appears to trace itself back to an infection from South Africa). Infections can be very unstable -- changing quickly to a variation that is less contagious and the original version burning itself out.
For example, Nightingale (who the Canadian CFIDS society is named after), appears to have acquired an infection when she was on duty in the Crimean war in the 1850's. Chances are it was a rickettsia infection.
THE CFIDS EPIDEMIC started close to the time that a much higher degree of world travel became normal -- and thus risk of a novel (new) disease hitting an ignorant population increased. The "Icelandic Disease" is a classic example -- it is ascribed to the stationing of British and US troops in Iceland from 1940's onwards. The Iceland population was pretty isolated prior to this contact. With this disease, also appear other not seen before illnesses (common to the US and UK, but not to Iceland). If the infection is not acute, but chronic, it stays below the radar of the medical types for a long time. It was only in the 1960's that the big diseases got under enough control that sleeper illnesses started showing up on the radar.
The Inclince Village outbreak appears to have been brought in by a South Africian visitor (See Olser's Web, the book). In this case, the infection also appear to cause a rare form of cancer which had an abnormally high incidence in these PWCs.
It is simply a mild variant of what smallpox did to the Indian. In the great flu epidemic in 1918-20, flu killed entire native villages in Alaska, and the same was seen in all populations that were isolated from prior flus.
Historically, you had many similar prior cases with troops returning from overseas --- and those infections appear not to be human-to-human transferred (mosquitoes, ticks) so they did not enter the general population, and they were forgotten or written up in some obscure military medical journal. With the Gulf-War we've seen this illustrated, except some of the infections do transfer to the servicemen families. With Vietnam, the use of Agent Orange has probably hidden similar cases.
More recently, the Gulf War introduces new infections into the population.
plus Vitamin D Deficiency
The second part is the growing Vitamin D deficiency caused by reduced regular exposure to sunlight. Our work place has changed. It has been suggested by some studies that "Type A" and the brightest folks are more inclined to CFS/FM -- well, these folks are also the most inclined to have indoor jobs and the least exposure to sunlight. Vitamin D is an essential component for the immune system. A mildly crippled immune system will not eliminate new novel infections.