Definition of hit the sack Hit the sack

We found 2 definitions of hit the sack from 2 different sources.

What does hit the sack mean?

Verb
hit the sack - prepare for sleep; "I usually turn in at midnight"; "He goes to bed at the crack of dawn"
		go to bed, turn in, bed, crawl in, kip down, hit the hay, sack out, go to sleep, retire
		arise, get up, uprise, turn out, rise result or issue; "A slight unpleasantness arose from this discussion"
		bed down, bunk down go to bed; "We bedded down at midnight"