Oh boy, I can totally relate to almost everything you wrote.

For me, the feeling of nausea is basically the same as the feeling of anxiety. My body cannot tell the difference. So when I feel the tiniest bit nauseous, I get very anxious and so the feedback cycle begins. It really sucks. And as you said, the fact that you know it is irrational on an intellectual level does almost nothing to help the physical symptoms of anxiety. I find that the breathing exercises and calming self-talk sometimes makes the problem worse because I just focus on the fact that I'm feeling sick. So distraction for me is the best thing to do. Unfortunately, when this feeling strikes when I'm on a crowded bus at rush hour, there isn't much I can do to distract myself.

Sometimes a pill is really the only thing that will help and remember that there is nothing wrong with that.