Earlier quoted context omitted.
But yes, pain is how your brain protects your body. Pain means you need to rest before your tissues literally rip to pieces from a structural failure.
No, pain isnt always due to structural or physical damage. That is what functional pain is. In many ways it is much worse than physical pain.
To me, it seems it's a theory to compensate for medical imaging technology that has far too low resolution. Doctors hate admitting that they don't know what's wrong, so instead they claim that the patient is crazy in politically correct terminology with an excessive number of syllables.
Structural tissue damage starts at a molecular level that cannot be seen by medical imaging technology. The fascia alone is too thin to be imaged at all, and so is completely ignored.
Biochemists have delineated in explicit detail how tissue breaks down at the molecular level. And they can reverse it. We need to start listening to them more.