Be swept off (one's) feet phrase
To fall in love with someone quickly and strongly; to become greatly admiring of someone; to be particularly impressed or charmed by someone because you have a very strong feeling of love for them.
I was completely swept off my feet at how attentively he treated me.
When he poured his heart out with a confession of love, she was swept off her feet.
He was swept off his feet at her exotic beauty.
Wholly enamored (of someone)
This phrase dates from about 1900.