From Longman Dictionary of Contemporary Englishbe/fall head over heels in lovebe/fall head over heels in loveLOT/VERY MUCHto love or suddenly start to love someone very much Sam was head over heels in love with his new bride. → head
Examples from the Corpus
be/fall head over heels in love• It wasn't just the usual liaison: the two of them fell head over heels in love. 