Head over heels is a rather disorienting phrase that began as the now-obsolete heels over head.
Head over heels made its debut in English in the early 15th century. It had the more literal meaning of taking a bad fall where you flipped or somersaulted and your head went forward over your heels.
It wasn't until the mid-1800s that we began to figuratively fall head over heels. Rather than describing tumbling over, it took on the metaphorical sense of being so infatuated with someone that you feel like you're somersaulting or falling. This popular idiom is closely related to our use of falling for someone and falling in love with someone.
Head over Heels is the title of films from 1922, 1937, 2001 and a 1979 film (AKA Chilly Scenes of Winter).
It is the title of albums by the Cocteau Twins, Cornerstone, Paula Abdul and Poco, and is the title of songs by ABBA, The Go-Go's, Switchfoot, and (my personal favorite) "Head Over Heels" by Tears for Fears.