sweep or carry or knock off someone's feet. Overwhelm someone emotionally; infatuate someone; make a very favorable impression on someone. For example, Winning first prize knocked her off her feet, or With his little gifts and gallant behavior, he swept her off her feet, or That fine speech carried him off his feet. The term using sweep dates from about 1900, carry from the mid-1800s, and knock from the early 1900s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.