Hit the Sack

A literal description of an old, uncomfortable-sounding mattress. Before modern bedding, many mattresses really were sacking cloth stuffed with hay or straw. The related phrase "hit the hay" came first, documented before 1880 and originally describing sleeping in a barn near the farm's actual hay store. "Hit the sack" in its modern sense took hold in the 1940s, popularised by American soldiers during the Second World War, who borrowed military slang for a sleeping bag to describe turning in for the night.