Illness is the state that is perceived by the individual when he is suffering from disease or other disorders. It is an awareness of being unhealthy and is more abstract than the simple presence of symptoms, which is a manifestation. It includes the distress and discomfort associated with disease and the psychological response to the presence of disease.
In 1994, roughly one in three people in Europe suffered from a long-term illness, and on any one day more than half the population will be taking a drug of some kind.
The man is not sick because he has an illness, but has an illness because he is sick.