It isn't just that the suffering from mental illness is real, it causes very real physical health issues and deeply disrupts your body's hormonal makeup via the HPA axis.

The strict delineation between physiological and psychological illnesses is mostly a Western construct and the unfortunate effect is that the CFS community has an obsession with proving that it is a 100% physical illness without any mental component. It shouldn't be necessary for them to assert that for them to be taken seriously. The same can be said of chronic Lyme, Fibromyalgia, IBS, many kinds of chronic pain

One fascinating thing is that there are people with non-physiological dissociative seizures (classified as a DSM mental illness). This population is actually much less likely to admit that their mental wellbeing has an effect on the incidence of these seizures than patients with conventional ones