I remember when I was around 18 when a very beautiful woman came to ask me something, I remember all of sudden a feeling of petrification - I just couldn't breathe exactly. I answered her (didn't stutter or anything) but I couldn't move. I knew the woman, and she wasn't always that pretty, but that day she was, and it was a very strange feeling. It was the definition of taking your breath away.
I wonder why does beauty do that? What makes it so terrifying? Why does beauty take your breath away? Perhaps that's also why women are likened to snakes.

Comparing it with reading a brilliant idea or understanding - which though is also somewhat terrifying, gives more the feeling of being in a whirlwind.

Part of what is so strong about your story, M, is "...but that day she was." Well spoken, like someone who has been close enough to beauty to see how it waxes and wanes constantly, even in the same person. There is a passage in one of my favorite books which I think comes closer than anything I know to describing the way it feels when the mood comes on.  I'll look for it (perhaps someone else will recognize it from my description and find it first).

"The second lasted five minutes; then the door opened and in came Angelica. The first impression was one of dazed surprise. The Salina family all stood there with breath taken away; Tancredi could even feel the veins pulsing in his temples. Under the first shock from her beauty the men were incapable of noticing or analyzing its defects, which were numerous; there were to be many forever incapable of this critical appraisal. She was tall and well made, on an ample scale; her skin looked as if it had the flavor of fresh cream, which it resembled; her childlike mouth, that of strawberries. Under a mass of raven hair, curling in gentle waves, her green eyes gleamed motionless as those of statues, and like them a little cruel. She was moving slowly, making her wide white skirt rotate around her, and emanating from her whole person was the invincible calm of a woman sure of her beauty."