It would appear that at some point after World War I, real mental health became something of a luxury. The absence of any real mental disease like schizophrenia or dementia certainly is not an indicator of complete mental health any longer. The boom in knowledge of human psychology that began in the 1960s has made that eminently clear.
Truthfully speaking, even basic functionality can no longer be automatically assumed for a human being living in the present age. There are an unprecedented number of Americans and Europeans undertaking psychotherapy today what started off as a fad now seems to have become a necessity of daily living. The pressures of the rat race are overwhelming. The number of situations and triggers for mental disorders has multiplied significantly. The stress levels are extremely high.
We are, therefore, reduced to defining acceptable mental health in very broad terms. A certain degree of aberration is to be expected in almost every post-modern human being. Reasonable mental health will, therefore, have to be defined by the lack of gross disorders. A good standard for judging this would be the one apparently employed by health insurance companies, who are reluctant to pay for mental disorders that do not result in complete breakdown of normal life for the individual.
The diseases that indicate a major disruption in mental health would today include Bipolar Disorder, Schizophrenia, or a major depressive disorder. Further mental disorders that may or may not be considered as mere a lack of fine tuning by authorities may include obsessive-compulsive disorders, alcohol or drug addiction, or stress-induced nervous breakdown.
Mental health in the twenty-first century means a reasonable quality of life and functionality in individuals, despite the overwhelming odds against them.