I've had Hashimoto's for some years now, and while I had some general symptoms of tiredness/exhaustion, along with depression, until it was diagnosed and I started on thyroid hormones, it was nothing like the ME/CFS which my ex-wife contracted living in Tonga in the early '80s.
It's the difference between feeling listless and "low" and not having much energy to do anything, in the case of hypothyroidism, versus being almost unable to stand up from a chair, in the case of CFS. Being wiped out for days by trying to do just a little exercise, as described in that article, is really characteristic.
My theory, since everybody seems to have one [cough], is that ME is an unrecognized emergent viral disease.
My ex-wife unquestionably caught it in Tonga, where she was doing field research in anthropology, and Tongans immediately recognized that cluster of symptoms as the disease "fakamahaki", if I remember the name right. (They attributed it to hostile ghosts, and believed it was usually contracted by going too near a graveyard at night - but the point is they recognized that same group of symptoms as constituting a specific disease.) The earliest recognized outbreaks of ME, and the early descriptions of it in Western medicine were in New Zealand, which has a large population of Polynesian expatriates, particularly Tongan and Cook Islanders; some of the early US outbreaks were in Southern California, which also has a large number of Polynesian expatriate communities.
If ME/CFS is caused by a virus or other infectious agent with a very long latency period, which some people's immune systems (perhaps most people's) are able to fight off successfully, that would explain an awful lot about it.