Once behavior disorders were thought to be due to diseases of the nerves themselves. This explains such term as “nervous”, “nervous breakdown”, and neurasthenia, which means nerve weaknesses or nervous exhaustion.
Today, we know that mental illnesses rarely involve any changes in the nerves themselves. Such illnesses may be due to organic conditions or changes in the brain itself and affects a great deal in overall mental health.
More common, however, are functional mental illnesses due to environmental influences and to problems caused by internal conditions. Among these conditions are such things as stress, tension, and emotional conflicts.
Functional mental illnesses are also called psychoneuroses, are the most common forms of mental illness. They relate to environmental conditions and problems and resulting stress, anxiety, and other reactions. Neuroses range from mild nervous conditions, fears, apprehension, and depression to severe states, emotional conflicts, personality disorganization, frustrations, and panic.
Character disorders is a form of mental illness that is marked by persistent personality disturbances and abnormal behavior. Individuals with character disorders do not adjust to society, cannot cope with problems, and are incapable of conforming to social standards.
A psychosis is a severe form of mental illness where the personalities break down completely. These are disorders most people think of as insanity. The sufferer loses touch with reality and retreats to an unreal world. He may drift in and out of his unreal world.