When people fall “head over heels” in love, their world has been turned upside down by romance.
The word fallen suggests helplessness, and the metaphorical “head over heels” is intended to expand the illusion.
However, consider that having your head over your heels is, in fact, the normal standing position!
You can blame American frontiersman, U.S. congressman, and Alamo martyr Davy Crockett (1786-1836), among others, for turning the phrase around.
When the expression first appeared around 1350, it was “heels over head.” In his 1834 autobiography, Crockett wrote: “I soon found myself ‘head over heels’ in love with this girl.”
So the phrase has been “head over heels” ever since.