I think physical and mental health are a compliment to each other. You can not be "Healthy" is either of this not good. Unfortunately, a large set of people do not have awareness of mental health and hence, this gets no notice.

20% of the U.S population has a diagnosable mental health issue at some point in their lives. Healthcare professionals say we need "mental hygiene" habits to maintain mental wellness. It is not so simple, just as maintaining physical wellness is not so simple. Mental hygiene includes stress management, opportunities for self expression, ability to acknowledge one's own feelings and to address them and other factors. The mind, body and spirit are one. We do not achieve physical health or call ourselves "healthy"unless we attend to all parts of ourselves.

It is very important for a person to be mentally healthy in order to achieve the healthy tag because if a person's mental health is not good i.e. if he or she is in a state of frustration, stress, anger, depression then ultimately it will effect his or her personal life and overall health of that person.
The indicators of a sound mental health are:

1. The person lives in reality rather than fantasy.
2. Solves most of the problems on his own and make his own decisions.
3. Can give and accept love.
4. They are more responsible.
5. They are emotionally mature.
6. Socially adjustable.
7. Normal attitude towards sex and does not suffer from any sex abnormalities.
8. Can take proper decision at proper time.

http://www.psychologydiscussion.net/health-psychology/characteristics-of-a-mentally-healthy-person/2072

I could resume my opinion in a sentence: mens sana in corpore sano... this is a latin sentence initialy from the poet Juvenal and its mean at the begining was more related to the need for praying to have a balanced spirit in a balanced body. Now a day, the meaning of the sentence have turned in what I really belive.... we need a to have a healthy mental state to be healthy. Moreover, the mental health can be improved using yoga in cancer patients and it usually help to recover better from cancer treatments.

Health- a state of complete physical, mental, and social wellness, not merely the absence of disease or infirmity. (Defined by WHO)

Mental Health- is a state of emotional, psychological, and social wellness evidenced by satisfying interpersonal relationships, effective behavior and coping, positive self- concept, and emotional stability.

• A person is mentally healthy when a person possesses knowledge of oneself; meets one’s basic needs; assumes responsibility for one’s behavior and for self-growth; has learned to integrate thoughts, feelings, and actions; and can resolve conflicts successfully.
• A mentally healthy person maintains relationships, communicates directly with others, and respects others.
• A mentally healthy person adapts to change in one’s environment.

Factors influencing a person’s mental health
-individual or personal
-interpersonal or relationship
-social or cultural

Mental disorder- a clinically significant behavioral of psychological syndrome or pattern that occurs in an individual and that is associated with present distress or disability or with a significantly increased risk of suffering death, pain, disability, or an important loss of freedom. (American Psychiatric Association, 2000)

General criteria to diagnose mental disorder:
-dissatisfaction of one’s characteristics, abilities, and accomplishments
-ineffective or unsatisfying relationship
-dissatisfaction with one’s place in the world
-Ineffective coping with life events
-lack of personal growth