There are a number of factors involved in an individual's health. For physical health, diet and nutrition; exercise and fitness; self care and hygiene; stress management; and genetics and heredity all play key roles. Most individuals are able to control most of these factors (except for genetics), and hence remain in reasonably good health.
Emotional and mental health mostly rely on stress management; a person who feels safe from harm and is able to manage stress in his or her life will tend to be in much better emotional and mental health than one who is not. Being physically healthy helps an individual remain emotionally and mentally healthy as well, and vice versa; the three factors are intertwined to some degree.
Medical attention is important to health. An injury or disease that cannot be taken care of by the individual most likely requires the prompt attention of a medical professional. Doing so will ensure that the condition can be halted from getting worse, and that the individual begins recovery towards good health as quickly as possible.
But a healthy individual should not wait for an illness or injury to seek medical help. Doctors and other medical professionals can also conduct a wellness exam to ensure the individual is healthy and also to screen for possible health problems down the road. In this fashion, a potentially serious or even deadly condition may be discovered and treated before it can become worse.