Head over heels
Meaning: Helplessly enamored
Originated in: 🏴 England
Heels over head
To be head over heels in love is to be hopelessly, recklessly in love with someone. The image conveyed is that you are helplessly tumbling forwards, unable to control yourself and merely a victim of romance.
It derives from the much more logical original phrase “heels over head”, as you would actually be when you tumble upside-down. This was used literally for physically being knocked over though. For some reason, the phrase was flipped around in the 18th century and began to be used metaphorically. Despite not making any sense (your head is normally far above your heels), the new version stuck, and it is now the only version used.