From Longman Dictionary of Contemporary Englishhit the sackhit the sack (also hit the hay American English) informalSLEEP to go to bed → hit
Examples from the Corpus
hit the sack• I'm bushed. I think I'll hit the hay.• I'm ready to hit the sack.• Then the two cups of decaff before you hit the sack.• Your husband needs to relax before he hits the sack.• Usually I come home, eat dinner, watch a little TV, and then hit the sack by 9:30 or 10:00.• When they do, they hit the sack for marathon love-making sessions - that's once Bill's made the bed!hit the sackhit the sackold-fashioned informalSLEEP to go to bed It’s one o'clock – time to hit the sack. → sackExamples from the Corpus
hit the sack• Your husband needs to relax before he hits the sack.• When they do, they hit the sack for marathon love-making sessions - that's once Bill's made the bed!• Then the two cups of decaff before you hit the sack. 