1. That can happen, sudden and subtle that is. It could have been something the dentist didn't notice before because it was hiding behind something else. Just a thought. Apart from that, my only other advice is to find another doctor whose office isn't going to give you so much stupid shit and will work with you. Or, worst case scenario, go to the ER and pitch a fit.

2 & 3. Can you talk to your supervisor or somebody at your place of employment about your concerns? Really. If it's getting to you that badly, it's best you bring it to somebody's attention before it devolves into you purchasing a gun and going postal. (I know you wouldn't actually do that, but the image of you doing so makes me giggle.)