Head over heels

[flashpig]

Surely this is always true. Why is it used?

[Quizmonster]

If you click here, that will link you to a web-page which explains.

[nirvanafarma]

So we're in france, la revolucion, the guillotine; occasionally because there was so much gristle on the back of an aristocrates neck when the blade came down it would catapult the aristo into the air, bust his neck and send his head flying over his heels.