Bipolar for 25 years here: mixed states get more common as you become more tolerant to your medication - frighteningly so in fact. The euphoria that comes with highs doesn't happen as before, leaving you wired and irritable but with the energy to do stupid things to yourself and others.

I haven't ever been suicidal but this last year I've allowed myself to think about it because of the complete pointlessness of just about everything I've done (or more commonly, not done because it was pointless). Sigh.