I know someone with bipolar II, and yes, having a diagnosis makes all the difference. Bipolar II is easy to misdiagnose, I think - the depressions are the most noticeable, but they come and go, and yet the highs are not as... prominent as with Bipolar I. For a long time he thought he just got depressed occasionally, no real rhyme or reason to it. In retrospect, and knowing the diagnosis, a lot of things made perfect sense.

His family history looks an awful lot like yours, too >_> <_<