from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To fall asleep, usually from implied exhaustion.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- v. prepare for sleep
Outgrowth of the earlier idiom, to hit the sack, with possible influences from other senses of to sack (tackle, pillage), and to sock (hit, slam), providing an implication that sleep has been thrust upon a person. (Wiktionary)