“head over heels”意为“神魂颠倒、从头到脚、完全地、全部地”，这个短语源自翻筋斗游戏。

【例句】
They are head over heels in love.
两人的恋情已到了神魂颠倒的地步。

It's obvious that those two are head over heels in love.
很明显，那两人已经深堕爱河之中。