When we break the word 'disease', it comes through as 'dis' and 'ease' -- something that is not at ease. Anything which makes you can cause you a disease. Anything that can cause you a problem and a normal human being can see it through normal naked eyes like a physical problem, for instance, high fever that can be seen through temperature, or cancer, or diabetes are all physical problems. In short, anything that we can see or feel through our eyes is a physical problem. And this is the reason why mental health is never considered as important as physical health because it is never seen.