Both being types of manic depression, the difference caused by both types lies in the severity of the manic episodes of each type. Bipolar 1 which common diagnosis of bipolar disorder you experience a full manic episode which lasts for a period of 1 week/longer that interferes with your daily functioning thus you may end up being hospitalized while with Bipolar 2 you experience a hypomanic episode(a period of mania which is less severe) and last for a period of 4 consecutive days. Bipolar 2 is often misdiagnosed as depression because you experience a depressive disorder that may last for about 2 weeks.