While our understanding of human behaviour is far from complete, it has improved over time. We now know that epilepsy is caused by abnormal electrical brain activity. People who experience epilepsy were once considered insane and confined to asylums.
Psychologists and psychiatrists may diagnose a mental illness if behaviour deviates greatly from social norms. They observe whether the person is experiencing extreme distress, or is placing their safety or that of others at risk.
Diagnosis is complicated and difficult, and involves some subjective judgment. People with mental illness are often confronted by social stigma and prejudice. However, almost half of all adults will experience a period of mental illness during their lives.
Mental illness is not always easy to identify. It does not fit the misconceptions and stereotypes of what was once called insanity.