Bipolar depression, here. I really wish that I had type I instead of type II bipolar disorder. Type I is the traditional, well-known sort. My kind, bipolar depression, has mostly long periods of the "down," which isn't a "sad" depression(for me, at least), but a complete lack of emotion, drive, or motivation for anything. When I have a really bad down, I don't care enough to get out of bed or eat. If someone puts food in front of me, I'll eat it, but I don't care enough one way or the other, or have the drive, to really do anything. I just feel nothing at all. To make a nerdy reference, it's like being Tranquil in Dragon Age. Best way I can put it.
The highs are very short, infrequent periods of super high-functioning creativity. I love them. On a high, I thought up and wrote a ten-page paper for a 400-level college course(USA here) in four hours, got an A, and a recommendation from the professor to publish the paper in an academic journal.
As much as I love the highs, they're infrequent and don't last long. Because of my bipolar disorder, I've been put on medical leave from college due to failing my classes(from not going) three times. All of my grades, from middle school through college, are either As and Bs or Fs. I either do the work and excel, or I don't care enough to do it and end up failing due to incompletes.
If I could get rid of it, I would, in a heartbeat. As nerdy as it is, I'm actually loving the Tranquil comparison now that I think of it. Imagine if you were tranquil, but every once in a while your emotions returned in this wild, great burst, but you know that soon you'd be tranquil again.