Advocate for yourself. I agree it seems like they are just throwing things out there. Ask why he thinks you are bipolar and if it seems off base tell him so. Let his reasons sink in a bit so that you can see if they really fit you. If they don't, challenge him. You need the proper diagnosis to get proper treatment. It's not like throwing spaghetti at the refrigerator to see if it sticks.

And yea, vent here. Vent there a bit too if it isn't going to get you into trouble.