Falling arse over tit for someone doesn't really have the same Thespian quality to it
Yes, but if you fall head over heels for someone - it doesn't suggest you're really falling. Heels over head would indicate a change in the equilibrium.
If you fall arse over tit, then the very nature of your arse being positioned higher than your tits would indicate there has been an upset to your balance.
I've fallen arse over tit for people in the past. I've been an arse and made a tit out of myself too.