The phrase upside down is so common in English that hardly any thought is given to it as far as its origin or its meaning is concerned.
However, a person beginning to learn English may think such a phrase is strange and may wonder what it means, so that is why an entire post is dedicated to explaining it.
The phrase “upside down” is most accurately translated as “de cabeça pra baixo.” As far as experts can tell, the phrase originated in the Middle Ages along with other similar phrases that meant turning something over on its head.
Originally, the phrase was “up so down” which meant “up as if it was down” or “turned so that the upper surface becomes lower.” Eventually, “up so down” evolved into its current form of “upside down.”
Here is an example of how this phrase is used:
http://www.youtube.com/watch?v=3qHA366oRMs&feature=related
(see 0:07)
