Definitions
1.adjectiveHopelessly smitten, madly in love.
2.adverbTumbling upside down; somersaulting."She tripped and rolled head over heels down the hill."
3.adverbAt top speed; frantically."Hearing the noise in the dark, the children ran head over heels back home."
4.adverb(usually with in love) Hopelessly, madly, to distraction, deeply, utterly.