I personally lean towards "Fibromyalgia" not being a distinct condition,
I have Fibromyalgia and I fit the 1990 criteria, 2010, 2011, and 2016. When one doesn't have the disease they can't believe it is real. But when you have it you know it is real and the criteria fit. And it is the same with ME/CFS and you have been diagnosed with it. You know when you fit the criteria, that it is real, and that the criteria fit.
I’m not convinced that the evidence for exercise being effective in fibromyalgia is much stronger than for us. (Although I get the impression that there is less patient evidence of harm.)
I was Dx'd with Fibro 2 years before CFS (as it was referred to back then) but I had already been told to walk for my Fibro dx. And then no one stopped me from walking when I got the CFS diagnosis. And then 2 years later I imploded due to the ME/CFS. Perhaps it was not good for Fibro either, but I now know for certain that it was not good for the ME/CFS.
I have IBS with constipation. I have had an colonoscopy and blood test to check for celiac and any other damage that could have resulted from any other condition or disease. Nothing. When you have IBS, you fit the criteria.
Too many doctors are not running tests to check for other conditions and do not follow criteria for the disease they are diagnosing you with. Pain is not the only symptom with Fibro and that is where doctors are erring. They don't care to run test after test and refer patients to specialist after specialist to track down what is really going on. In the US, doctors are up against insurance companies.
Muscle pain (different than the tender points areas), IBS, fatigue/tiredness (and as we know, it is PEM and not fatigue or tiredness in ME/CFS), thinking or memory problems, muscle weakness, headache, numbness/tingling, dizziness, insomnia, (and RLS and sleep disturbances) nervousness, constipation, chest pain (costochondritis), dry mouth, itching, ringing in ears, dry eyes, shortness of breath, rash, sun sensitivity, easy bruising. And I fit whichever criteria one follows. I onset gradually with Fibro at puberty.
The 2010 criteria list these conditions clearly and even more on page 3, some I don't have but I certainly have enough of them. And page 1 where you check off where you have felt pain, well, don't get me started. I have everything but the Abdomen and left Jaw. I also have severe menstrual cramps which are also known to happen with Fibro.
Again, I had Fibro first and then ME/CFS five years later after mono. You have to live it to know the diseases and understand the difference.
Some might argue how can you tell the difference between Fibro and ME/CFS. PEM. And Fibro has that pattern of pain that usually does not fit ME/CFS.