Hi there

Bipolar disorder is actually a very complex mood disorder to define.  One cannot diagnose themselves.  Everyone has their moments of feeling like they are on an emotional rollercoaster.  But usually with Bipolar Disorder...the fluctations are extreme and cause great disruptions in one's life. 

Health Central does have a very good Bipolar site which you may want to check out here.  The basic definition our site gives is this: 

"Bipolar disorder, or manic-depressive illness, is characterized by moods that swing between two opposite poles:

• Periods of mania with exaggerated euphoria, irritability, or both
• Episodes of depression "

I hope this helps some.  Thank you for your question.