Imagine, if you can, living an emotional see-saw, wherein you experience two very different and unrelated emotions, each for several weeks at a time.  One emotion is ultimate darkness and despair, while the other emotion is an elevation to feelings of being invincible, whether experienced positively (feeling utter elation) or negatively ( feeling utterly irritable and confrontational).  While for some this sounds unfathomable, this is a very real mental illness that 1% of the population will deal with at some point in life....it is called Bipolar Disorder.
        Bipolar Disorder is a Mood or Affective Disorder, which in its grossest definition, is characterized by the presence of Manic or Hypomanic Episodes accompanied by Major Depressive Episodes.  The name Bipolar Disorder refers to the vacillation between the poles of depressed and manic behavior experienced by an individual with the disorder.   Another common name for Bipolar Disorder is Manic Depression, and the individual who experiences a shift in affect or mood is usually said to have had a "mood swing."

        Bipolar Disorder has a history which spans back to the development of the Hippocrates-Galen Humoral Theory of Ancient Greece and Rome.  Hippocrates maintained that mental illness was the result of the action of natural body fluids ("humors") on the brain.  The four humors which Hippocrates focused on were blood, phlegm, black bile, and yellow bile.  At the very beginnings of the diagnostic system, mania and melancholia were two of three types of diagnoses, but mania was conceived of as being more like today's Schizophrenia.  Hippocrates recognized that melancholia and mania were brain disorders, but he did not combine their effects to define one single disorder, Bipolar Disorder (Zuckerman, 1998).  During the Middles Ages and Renaissance, some physicians made mention of a melancholia which transformed into mania (Zuckerman, 1998).  It could be argued that this was the first true reference to Bipolar Disorder in the history of mental illness classification.  By the close of the 19th century, Emil Kraepelin coined the term "manic-depressive psychosis," thus emphasizing the link between melancholia and mania (Zuckerman, 1998), and the term "manic-depressive" remains prominent in the language of mental illness today.
        Bipolar Disorder refers to a group of Mood Disorders within the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (APA, 2000).  This group is comprised of Bipolar I Disorder, Bipolar II Disorder, Cyclothymic Disorder, and Bipolar Disorder Not Otherwise Specified.

      Bipolar Disorder is characterized by two mood states that are on opposite ends of the spectrum.  Please note, for a more detailed list of diagnostic criteria, you may refer to the Harvard Bipolar Research Program website.

        Major Depressive Episodes are Characterized By:

•      Depressed Mood
•      Loss of interest or pleasure in activities that usually are pleasurable
•      Significant weight loss or weight gain, or a marked increase or decrease in    appetite
•      Difficulty sleeping or sleeping significantly more than usual
•      Restlessness or slowed down motor functioning as observed by others
•      Loss of energy; constant fatigue
•      Feelings of worthlessness, excessive guilt
•      Difficulty concentrating; difficulty making decisions
•      Recurrent thoughts of death, suicidal ideation, or suicide attempts

       Manic Episodes are Characterized By:

•    A distinct period of abnormally elevated or irritable mood
•    Inflated self-esteem or grandiosity
•    Decreased need for sleep
•    Increased talk or pressure to keep talking
•    Subjective feeling that thoughts are racing
•    Easily distracted (more so than usual)
•    Increase in goal-directed activity
•    Excessive risky behavior (engaging in pleasurable activities with a high            potential for painful consequences), such as unprotected sex with many partners; unrestrained buying sprees.