I heard that as a theory once for what might be the cause for ME/CFS.
That something causes the body to always be in fight-or-flight, never in rest-and-digest. And that just drains the body and leads to pains, because the body never properly recovers/heals. Which can also lead to a vicious cycle, where these new pains reinforce the fight-or-flight response.

It is just one theory, though. We don't even really know what ME/CFS is, and whether it is just one illness, or rather multiple ones with similar symptoms...