Head over heels
Excited, and/or turning cartwheels to demonstrate one's excitement.
'Head over heels' is now most often used as part of 'head over heels in love'. When first coined it wasn't used that way though and referred exclusively to being temporarily the wrong way up. It is one of many similar phrases that we use to describe things that are not in their usual state - 'upside-down', 'topsy-turvy', 'topple up tail', 'arse over tea-kettle', 'bass-ackwards' etc.
Herbert Lawrence's Contemplative Man, 1771 is the first known citation of 'head over heels':
"He gave [him] such a violent involuntary kick in the Face, as drove him Head over Heels."
The first mention of love comes after the time that the phrase had crossed the Atlantic. This example, from the Indiana newspaper The Lebanon Patriot, June 1833, and the lack of quotation marks or explanation suggests that the expression was in common usage by that date:
About ten years ago Lotta fell head over heels in love with a young Philadelphian of excellent family.
'Head over heels' is a good example of how language can communicate meaning even when it makes no literal sense. After all, our head is normally over our heels. The phrase originated in the 14th century as 'heels over head', meaning doing a cartwheel or somersault. This appeared later in Thomas Carlyle's History of Frederick the Great, 1864:
"A total circumgyration, summerset, or tumble heels-over-head in the Political relations of Europe."
Another note: Carlyle's spelling of summerset for somersault. John Lennon reinvented that in 'Being for the Benefit of Mr. Kite' - "Ten somersets he'll undertake on solid ground."
'Head over heels' isn't alone - many everyday idioms make no literal sense. Another nice example is 'putting your best foot forward'. Anyone trying that should arrange to have at least three legs. We humans should limit our efforts to 'putting our better foot forward', unless we want to end up 'heels over head'.