It's normal to occasionally feel sad, happy, anxious, confused, forgetful or fearful, but when a person's emotions, thoughts or behavior disrupt their lives, they may be suffering from mental illness. According to the World Health Organization (WHO), about 450 million people worldwide are affected by mental, neurological or behavioral problems at any given time.

However, determining that someone has a mental illness, and which one, is one of the challenges mental health professional face. One effort to catalogue these afflictions is the "psychiatrists' bible", the Diagnostic and Statistical Manual of Mental Disorders - the latest edition fills nearly one thousand pages and lists over 400 disorders.... and counting.