Bipolar disorder is a disorder of mood and energy level with episodes, not swings, that generally last weeks to months in duration. Bipolar episodes are about broad mood states of depression and mania, while BPD mood swings are reactionary episodes, usually fairly brief by comparison, of very defined emotions such as anger, rage, sadness, rejection, abandonment. Mixed bipolar episodes are not episodes of quick swings between feeling good and feeling bad/irritable; they are states where full manic and full depressive symptoms are experienced concurrently. Most of the people I know personally or on PC who are diagnosed with bipolar disorder alone don't self injure or have issues of abandonment, etc., while those that do are generally also diagnosed with BPD.