My definition of being healthy is feeling a sense a well-being–not feeling physically or mentally out of sorts or feeling like I am sick. Nothing is out of whack so-to-speak. I do not have a fever, virus, or any type of sickness that would require a physician, medication or anything to get back to my state of well being. If you have cancer or heart disease you have an altered state of health and you are not healthy.
Illness however is not feeling quite right to put it simply. Sometimes it is just as simple as a cold, fever or minor disturbance but you know you do not feel like you normally would. A medical disease is an illness. The majority of diseases you can code are illnesses. Some are merely conditions–temporary states. You have an illness if you have a medical condition whether or not it is treatable.
I would not consider old age to be an illness, it is a stage of life everyone goes through. For some people it is a state of mind. Some old people think young and some young people are very old. It is not something you can treat like a cold or the flu. Spirit possession is not a illness because it can be in a person’s mind and not real. If a person is schizophrenic, they may think they are being possessed by a spirit but the schizophrenia would be the illness. That is not a healthy person, they have an illness, which can be treated. Menstruation is a condition that women get it is not a disease or a disorder. These are the three that are experienced but cannot be considered an illness that one would seek treatment for unless the symptoms surrounding them are a reason for treatment. Excessive menstruation could be treated and a person seeing things that are not there (spirits), may be a reason to initiate treatment for the underlying symptoms such as delusions.