Here's a breakdown:
* Giddy: In this context, it's not about being dizzy or lightheaded. It's an old-fashioned word meaning lively or spirited.
* Up: This simply means to move forward or accelerate.
So, "giddy up" essentially means "move with spirit and speed."
It's a common phrase used in western movies and literature, and it's also a fun way to encourage someone to hurry up!