Meaning:
1. To fall “head over heels” for someone is to feel a romantic interest for them.
2. Someone that had a bad fall. (e.g., He fell head over heels down the the stairs.)

The Origin Of ‘Head Over Heels’
By the looks of it, this phrase has an older, inverted form that goes “heels over head.” This inverted form referred to someone who had fallen down. For example, in the London Annual Register newspaper, printed on January, 1766, it reads:
“Being thrown with great vehemence from a projecting crag, which turned him heels over head, he fell down perpendicular upwards of fifty yards into a snow drift at the boot of a cliff, where he lay above half an hour before his companions could get to him to take him up.”
According to WorldWideWords, it was by the end of the 18th century that this idiom changed from the inverted version to “head over heels,” the one people are familiar with today. This newer version referred to someone who had fallen, not on the ground, but in love. An example of this comes from a book titled A Narrative of the Life of David Corckett, 1834:
“I soon found myself head over heels in love with this girl.”
In short, this expression is at least 244 years old.
Example Sentences
- I’m falling head over heels for a woman at my job; she is pretty and has a great personality!
They are there to give you an idea on the expression’s age. For instance, if an idiom shows up in a newspaper from the year 1850 and it is quoted on here, this does not necessarily mean that it originated from that newspaper. What it does mean, though, is that the idiom is at least that old.