According to the World Health Organization "health" is defined as follow : "Health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity."
See : WHO
From a practical viewpoint, this means that just because you are not feeling pain or any other symptoms, does not necessarily mean that you are healthy. We can identify five degrees of health or illness between true health and death. These are:
Healthy – these people are indeed uncommon, as they have no strain on their biochemical or biomechanical systems and are emotionally and socially well-balanced and happy.
These people are also functioning in harmony with their environment – both locally and internationally.
Non-symptomatic – these people will not be aware of any discomfort or symptoms, however they will not be functioning at their greatest potential. They will still have physical, biochemical or emotional imbalances that their systems are coping with, at the expense of stress on their immune systems, psyche or physical bodies.
Clinically sick or ill – these people will be aware of being ill and have symptoms such as pain, discomfort or fever. They are not at death’s door and may have an illness as simple as the common cold or an aching muscle or joint resulting from an identified strain.
Critically ill – these people are usually in hospital, with medical personnel and family uncertain about their chances of survival.