A mixed episode (DSM-IV) is not a disorder itself, but rather is a description of a component of a specific type of bipolar disorder.
Like most mental disorders, a mixed episode must be severe enough to cause distress or impairment in social, occupational, education, or other important functioning and is not better accounted for by the physiological effects of substance use or abuse (alcohol, drugs, medications) or a general medical condition.
Note: The term “Mixed Episode” is no longer used in the updated Diagnostic and Statistical Manual of Mental Disorders (DSM-5). As of 2013, such episodes are considered a “specifier” of bipolar disorder. See updated “mixed features specifier” criteria.