What does 'hit the sack' mean?

What it means: To go to bed and sleep. An informal way of saying you're going to sleep.

"I'm exhausted — I'm going to hit the sack."
"Right, I'm hitting the sack. Night."

Where it comes from: "Sack" was old slang for a straw-filled sleeping bag or mattress. Workers and travellers would sleep on sacks. "Hitting" it meant throwing yourself down onto it. The expression dates to the early 20th century.

• "Hit the hay" — identical meaning, same origin (sleeping on hay)
• "Turn in" — British English, more formal
• "Call it a night" — specifically ending an evening
• "Crash" — informal, implies collapsing with exhaustion

Register: Casual. Use with friends and family. Too informal for professional emails.

Tags: idioms, sleep, everyday English, informal