Out of interest, did you ever come across the theory that ME/CFS is caused by EBV?
Yes, in fact, in the beginning of the CFS saga in the early 1980's, the evidence appeared so strong that EBV was the culprit, that it was often referred to CEBV, Chronic Epstein Barre Virus, or something like that. When they later discovered other viruses can also cause it, they began referring to it as CFIDS, Chronic Fatigue Immune Dysfunction Syndrome, which I think is likely a more accurate term than CFS, and perhaps even more accurate than the current ME/CFS.
What I've noticed over the years is that just about anything that traumatizes a person can bring on ME/CFS. I think the main culprit is the immune system becomes compromised by that trauma in some manner. I think we're all swimming in an ocean of microbes, most of which have yet to be discovered by modern science. When a person's immune system is healthy, these microbes are non-factors, and are easily tolerated, expelled or in some manner or another, taken care of, or eliminated. I think a person's ability to deal with stress is a very important factor in this whole scenario.
Interestingly, what really helped me turn the corner on ME/CFS was discovering a thoracic extension exercise I found on YouTube. I began to see significant improvements within just 3-4 days. The following :37 second video shows how a rolled up towel or foam piece can be used for the upper thoracic area:
Thoracic Towel Stretch
Below is a link to a 5-minute video which goes into more detail on how to use a towel or foam piece to loosen up the upper back:
The Simplest and Most Effective Exercise For Thoracic Extension
I don't know
exactly why this was so effective for me (which took me from 20-25% functionality for about 30 years, to about 75%). But I suspect it's because the nerve supply that runs from these vertebrae goes directly to the top part of the GI tract, which is primarily where the immune system of the body is located. I do know that in some kind of indefinable way, my immune system felt stronger and more resilient after starting this.
I think there are other factors involved in immune system health that should always be considered, such as diet, exercise, etc. But in my case, it appears improving the nerve supply going to my immune system area was key.