just my opinion, but it reverts us to child status and we remember that as a powerless time, we value our adult status a lot and don't like to see ourselves heavily dependent again -

It's something big, that happens to us involuntarily, and we cannot ignore it (and worse, cannot shut it off, we just have to endure it).

That's how someone defined shame - having your private self involuntarily exposed to others and you find that you're unable to defend against the exposure.

And it's especially awful to realize that we're hugely exposed to someone we hardly know (when you come down to it), and who knows so very much about us - it heightens the sense of vulnerability past a tolerable level.