As I understand it many PWME get orthostatic intolerance. That is easy enough to establish from symptoms.
From what I recall in the research, it's something like 95% of ME/CFS patients have NMH and/or POTS. So not just "many" but rather nearly all of us.
What worries me is that a tilt test may confirm 'greying out' really is orthostatic intolerance but it does not tell us the cause.
It can show specific blood pressure reactions to orthostatic challenge, which can give relevant specialists a good idea of what to try for treatment. Additional testing can also then be ordered to find a more proximate cause of the OI, such as norepinephrine levels, blood volume, certain auto-antibodies, diabetes insipidus, etc etc.
'POTS' is a technical term for a physiological effect and it may have many causes.
Most ME/CFS patients actually have NMH, not POTS. But POTS is better understood and easier to say, hence a lot of people with NMH talk about their "POTS" when it's not what they actually have. But that's a somewhat irrelevant matter of terminology, despite doctors often liking to shut down if a patient uses a technically incorrect term at any point
Any treatments used might relieve the symptoms in one case and not another. Moreover, symptom relief might go with a long term benefit in some but a long term adverse effect in others. If the orthostatic intolerance is a protective feedback response treatments might aggravate things long term. The point is that I don't think one can assume that treatments that are useful in one context are appropriate in the context of ME unless someone has done some careful long term monitoring.
With appropriate followup testing, it should be somewhat straightforward to decide on effective treatments to try. I think it's also a bit ridiculous to completely withhold treatment for a severely disabling symptom on the excuse that it might cause unexpected problems.
OI can and has left me bedbound for weeks at a time. Being forced to lie down all day is painful, frustrating, and really
really boring. It's well worth trying a reasonable treatment based on trustworthy test results, when that treatment can cause a drastic increase in quality of life.
Indeed, requiring that we KNOW the cause and KNOW exactly how the treatment will and won't effect us is a rather extreme requirement which I don't think is present in any other illness or even idiopathic and uncomplicated cases of OI. And it's that mindset which is leaving us untested and untreated for extremely debilitating symptoms.
Treating my OI has made the biggest difference to my symptoms thus far, and I only wish I was able to do it with active assistance and oversight from a local doctor.