Was possibly begging to go to bed? (3,2)

I believe the answer is:

sat up

I'm a little stuck... Click here to teach me more about this clue!

'bed?' is the definition.
Although both the answer and definition are past participle verbs, I cannot understand how one could define the other.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Another definition for sat up that I've seen is " Suddenly became alert".)

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.