> I think the situation is more akin to stomach ulcers, which everyone _knew_ were caused by stress, until of course a physiological cause was found.

Everyone knew that there were multiple contributing risk factors, including physiological, behavioral, and stress-related, for gastric ulcers before H. Pylori's contribution was discovered. And all those other factors are still relevant after H. Pylori, too, its just one added factor that wasn't known previously.

Your line of thinking is interesting. If you actually look at the research, you'll see that stress is still a factor in gastric ulcers (see for example http://www.ncbi.nlm.nih.gov/pubmed/25111233 and http://www.ncbi.nlm.nih.gov/pubmed/16581366). Just because H.Pylori can cause ulcers doesn't mean there can't be other causes. Given that psychological stress increases stomach acid, it's plausible that stress can cause ulcers.

A lot of CFS patients bring up the subject of stomach ulcers. It's almost as if they want to prove that psychosomatic illness doesn't exist.