The origin of the term isn't entirely clear, but it's thought to have come from the idea of being "bushed" or "beaten up" after a long journey or strenuous activity.
Here are some examples of how it might be used:
* "I'm bushed after that long hike. I need a nap!"
* "I'm so bushed from work. I can barely keep my eyes open."
* "Don't ask me to go out tonight, I'm bushed."