Head over heels

Neil: Hello and welcome to The English We Speak, I'm Neil and ... I am waiting for Li.
Li: Ouch. And I'm Li, here on the floor. I went head over heels but ... but I'm ready to present the programme, Neil.
Neil: Are you okay, Li? Let me help you up.
Li: Thank you. I appreciate you helping me to stand up.
Neil: I am sorry that you fell over like that. You sounded so cheerful ... so you are head over heels Li? Who is the lucky guy?
Li: The lucky guy? What do you mean, Neil?
Neil: Well, the one you are head over heels in love with. Is it anyone I know?
Li: Anyone you know? I don't know what you are talking about, Neil. I have just fallen flat on my face ... 
Neil: You said that you are head over heels. This is an expression we use in English to say that you had such a dramatic fall that your head was over your feet and we use it when we want to say that someone fell madly in love.
Li: Oh, that's when we say that someone has fallen head over heels for another person.
Neil: You can also imagine you are a gymnast doing somersaults or cartwheels. Your head goes literally over your heels.
Li: Yeah ... It makes sense: when you are in love it might mean that you are so happy that you feel like jumping around.
Examples
They met at a dinner party and fell head over heels for each other.
He is gorgeous! I am head over heels in love with him!
She is a hopeless romantic: she is always head over heels in love with somebody.
Neil: So, who is it Li? Who have you fallen head over heels in love with? I promise I won't tell a soul.
Li: Neil, I came here very excited to present a programme with you but I must say that now my head hurts ... 
Neil: Your head hurts?
Li: ... my feet are sore ... 
Neil: Your feet are sore? What's been going on?
Li: ... but I am certainly not in love with this bin that made me fall over.
Neil: Oh ... Okay. So no juicy gossip for us today. Well, we'd better say goodbye.
Li: No juicy gossip! And let's finish the programme because I'd better go and have an aspirin. Bye!