Illness refers to the presence of a physical or mental disease or impairment ; the experiences associated with disease that ultimately affect the person’s overall state of being and social functioning:
Illness is highly individual in that a person may have a serious disease but experience no feelings of pain or suffering and hence there seems to be no illness; conversely, a person may be extremely ill, as with a somatization disorder, but have no evidence of disease that can be measured by pathological changes in the body.