Hmm... I always thought tsundere was a severe an extreme case of bipolar disorder.
Tsunderes turn tsuntsun or deredere in reaction to stimuli.
Bipolar disorder is closer to unpredictable and is less episodic. Someone with bipolar disorder tend to be with certain plateau lasting hours, and certain times days, while you'll see a tsundere changing mood every 20 seconds or so.

Heh, I'm just pulling your leg. I think our definitions might be compatible.
Maybe, but would it really be teh interwebz if we didn't start pointless arguments?