The phrase "head over heels" is an idiomatic expression that means to be deeply in love or completely infatuated with someone. It suggests a state of intense emotional involvement, often associated with excitement and joy. When someone is described as being "head over heels," it conveys that they have lost their balance or composure due to the overwhelming feelings they have for another person.
The term "head over heels" dates back to the 14th century and originally meant to be upside down. The current meaning relating to love or infatuation evolved in the 19th century, suggesting a sense of turmoil and emotional disarray, akin to being turned upside down by strong feelings.