'Head over Heels '

One of my favourite topics is the origin of words and phrases , it will definitely veer more towards Middle Ages and Victorian origin words over the coming cold, wet and dark days where interesting outdoor blips are an exception . However as a starter for ten thought I would use a literal statement i.e. ' head over heels' - although My wife did say an explanation was definitely required as it did look a trifle 'odd' - if you know what I mean !