Yes, its a very strange thing to have in your aorta. An no, its not at all uncomfortable. Apart from the unpleasantness of having one's femoral artery punctured, most people don't find the experience particularly alarming. I have asked them; they cant feel the movements of the balloon. In any case, I am sure that any adverse components of their experience are drowned out by the appreciation of the fact that one is alive in spite of a massive coronary event.