What does it mean have “Serious Mentally Illness”?

Serious mental illness is a billing and diagnostic term defined as having at some time in the past year a diagnosable mental, behavioral, or emotional disorder that met the criteria specified in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) (American Psychiatric Association [APA], 1994), that resulted in functional impairment that substantially interfered with or limited one or more major life activities.

Serious mental illnesses include major depression, schizophrenia, bipolar disorder, obsessive compulsive disorder (OCD), panic disorder, post traumatic stress disorder (PTSD) and borderline personality disorder.