I don't know if it's normal, but it does happen. I used to be really short-tempered and irritable, but then I was diagnosed with ADD in addition to my bipolar and taking the meds for that has changed me for the better.

I think the right med balance helps with this, as well as giving yourself lots of personal space. Don't feel pressured and you will start to think of other ways of reacting than snapping someone's head off.