What is the Meaning of the Idiom
HIT THE SACK?

Definition:

go to bed to sleep

1. If you will excuse me, I am going to hit the sack. I have to get up early tomorrow morning.

2. Time to hit the sack, kids. You have school tomorrow.

3. I was so tired. I had hardly hit the sack before I was asleep.

Note: This has the same meaning as the idiom HIT THE HAY.

It comes from the time when beds were made of cloth bags filled with hay.