They are in this case. I think it's probably helpful to distinguish between "old school" mental illness (hysteria, neurosis etc) and "modern" mental illness (e.g. how depression, bipolar etc are treated these days). Wessely has long talked about CFS/ME as neurosis, or suggested mass hysteria with a modern angle.
In Wessely's own words on a related illness "Sufferers from mysterious condition that lie outside conventional medical practice no longer consider themselves to be oppressed by spirits and demons but by mystery gases, toxins and viruses. This is particularly visible in the changing nature of mass hysteria." http://www.cfsinfo.be/Documentatie/AA%20%20Strijd%20classifi...