Attested from the 14^th century onwards, originally as heels over head, which better rendered the notion of things being upside down (head over heels is the standard state of being).

• (America) enPR: hĕd ō'vər hēlz, IPA: /ˌhɛd oʊ.vɚ ˈhilz/, /ˌhɛd oʊ.vɚ ˈhi.əlz/
• (RP) IPA: /ˌhɛd əʊ.və ˈhiːlz/

head over heels (not comparable)

1. Tumbling upside down; somersaulting.

   Synonyms: arse over tit, ass over teakettle, base over apex

   She tripped and rolled head over heels down the hill.

2. At top speed; frantically.

   Synonyms: full tilt, full throttle, like mad

   Hearing the noise in the dark, the children ran head over heels back home.

3. (usually with in love) Hopelessly; madly; to distraction; deeply; utterly.

   Synonyms: head over ears

   • 1904, Henry Huttleston Rogers, “Letter from Rogers to Clemens (Mark Twain) dated 8 February 1904”, in Mark Twain's Correspondence with Henry Huttleston Rogers, 1893–1909, University of California Press, published 1969, page 555:

     I am head over heels in trouble.

• French: jambes par-dessus tête
• German: purzelnd, überschlagend, kopfüber
• Italian: gambe all'aria
• Portuguese: cabeça pra baixo, ponta-cabeça
• Russian: вверх ногами
• Spanish: cabeza abajo, patas arriba

• German: Hals über Kopf, wie verrückt, wie wahnsinnig
• Italian: a gambe levate
• Russian: сломя́ го́лову

• French: follement, éperdument, à la folie, fou
• German: kopflos, wahnsinnig, Hals über Kopf, (bis) über beide Ohren
• Italian: follemente, perdutamente, fuori di testa
• Russian: по́ у́ши
• Spanish: perdidamente

head over heels (not comparable)

1. Hopelessly smitten; madly in love.

• French: fou amoureux
• German: kopflos, wahnsinnig