IMHO, the similarity of symptoms in a bunch of illnesses:
M.E.; M.S.; organophosphate related ones; possibly Lupus and some others,
suggests to me that there is a single common "pathway" in the immune system being screwed up
and the variations in the initial cause and effects it *uniquely* has on the body over all, and then genetics, plus possible damage in various ways from environmental causes (long term heavy metal exposure for example)
possibly a retrovirus or the like being the prime thing that makes a specific weakness in the immune system "pathway"
results in a myriad of very similar health problems
We've been to used to the simple "mechanistic" dogma of the Cult of Health and Big Business, (indeed, of our societies):
one simple disease, one drug to cure it
Reality is NOT like that. There are always so many subtleties, synergies and knock on effects etc that have been overlooked.
A sort of simple and deadly example is the horrible cocktail of syphilis, HIV and Tuberculosis in the poor in the USA. Resulting in immune compromised and deeply troubled and screwed up people which then gives rise to extremely dangerous resistant and communicable TB.
Simple mechanistic experimentation in a laboratory will usually not show such things.
So, with the mindset of "simple obvious cause, then provide specific approved medicine to treat"
the medical Profession has had entirely the wrong view point about a lot of health problems.
Thus when a patient presents with something they cannot explain easily, the cultural stand by is: "well the tests cannot be wrong therefor the patient must be making it up!"
Which in real Science is bullshit: if you cannot understand something but are presented with clear obvious mass of evidence, then your Theories and/or detection/measurement equipment must lack, and then you work on it but do not dismiss it!
Took astrophysicists decades to work out what a quasar
probably is, and the smart ones will know they do NOT "know" what it truly is even now, just best evidence suggests what it probably is, until we can reach one and see it's formation with our own eyes there's no "proof", just evidence and hypothesis.
We don't know what diabetes truly is, as we don't know what causes the autoimmune attack, but we're getting closer. There is no cure as yet, but some therapies look like they may offer such in the foreseeable future. Not merely treatment, but actual cure.
that's after vast sums of money and research and decades of work on this very common deadly disease many Humans suffer from
The colossal arrogance and stupidity of dismissing "stealth"/unusual illnesses to the realms of "they are making it up", is outrageous