Pathologising life

If life is the slowest way we can die, could we say that all mental activity is a sign of mental illlness or unbalance?

General anxiety disorder used to be called " being a worry wart".
Depression used to be called malingering.

If behavior we used to consider bad is now but a sign of mental illness, then what constitutes mental health? If chemical unbalance defines mental illness, then what is the state of chemical balance? How do we know this?