Even today it is very hard to get an accurate CFS dianosis. Patients often are diagnosed with as suffering from a viral infection, or psychological, neurological, or immune disease. They almost always only get a CFS diagnosis after all the other treatments fail. I definitely would not be surprised if it turned out to be present in the past, but misdiagnosed.
One thing that certainly does not help is that the primary symptom of ME/CFS, post-exertional malaise, is counter intuitive. The pain and fatigue comes after a delay, which hides the cause and effect. Everyday physical activity can also be enough to bring back symptoms. This means that if you don't know what you are looking for then ME/CFS will appear to come "out of nowhere", like a mystery chronic illness.
I don't think severe limitations in physical mobility were as common in the past. I'm not the only one who thinks this. The creators of WALL•E clearly think it as well.
One thing that certainly does not help is that the primary symptom of ME/CFS, post-exertional malaise, is counter intuitive. The pain and fatigue comes after a delay, which hides the cause and effect. Everyday physical activity can also be enough to bring back symptoms. This means that if you don't know what you are looking for then ME/CFS will appear to come "out of nowhere", like a mystery chronic illness.