I know it means to go to sleep but where did it originate from. I'm looking for first use. Just curious.
Mattresses used to be stuffed full of hay, or were sacks full of hay. Thats why we say "hit the hay" or "hit the sack."
In the entry for sack on the Online Etymology Dictionary:
Slang meaning "bunk, bed" is from 1825, originally nautical. The verb meaning "go to bed" is recorded from 1946.
The OED has it from 1943 in James J. Fahey's Pacific War Diary, 1942-1945:
I hit the sack at 8 P.M. I slept under the stars on a steel ammunition box two feet wide.
It's in the same entry as the earlier hit the hay, from 1912 in Dialect Notes:
Hit the hay, to go to bed.
It means go to bed. Linen was once the common bedding material for sheets. Believe linen sacks/storage bags (like burlap bags/hessian bags today) were once more commonly used for things like grain (linseed in the old process of extracting linseed oil) etc. Linen (flax), also the same material/fabric as was used for bed linen/sheets, pillow slips and blankets etc. The word Sac in French is translated to sack or bag in English, also similarly to "sac" an action, as we use "to pillage" so to strip ruthlessly, to steal with force. This alludes to the age old marital tug of war, over who takes too much of the bed covers and leaves the other party cold and bare, like a plundered village, shivering in the cold night of winter.