In my opinion people have these mental disorders because they crave success and attention. If they don't get this, either because they don't know how or they just don't want to get it the way they are supposed to.(or in an appropriate manner) Then they resort to another way of getting it.
Sometimes people might crave success but they just can't achieve it so they resort to "self handicapping".
Self handicapping is where the person chooses to do something that is easy instead of hard so that they know that they will achieve success. Thus giving them attention. This method is also used so that they know that they will not fail at what they are trying to do. People want to be successful because they want credit and attention.
So to answer your question Boagie, Are all diseases of a reactionary nature. If you include mental disorders to be a disease then yes I would have to say that they are of a reactionary nature. I'm not sure about physical though.