To be completely healthy a person needs to be well physically, emotionally, mentally and socially. This means that the person should be free from diseases, be able to work efficiently lead a peaceful and satisfied life as well as live in harmony with his surroundings. A person may not be healthy even if he is not suffering from any disease since he may be scared of something or may not be able to perform his work efficiently.
Lets take an example - A person may be living in a society where there are continous conflicts and riots. So he will be constantly scared for his and his family's well being. In this case, he is not suffering from any disease, but he is in poor health due to social problems.