Image source: 1; 2.

Another way to say it is TO HIT THE SACK ;-).

This is a nice comic on this idiom made by Ploopikoosy:

More example sentences from the web:

• I have a busy day tomorrow, so I think I’ll hit the hay.
• Time to go home and hit the hay!
• I’m tired, I’m gonna hit the hay.
• Well, I’m going to hit the hay, I’m feeling pretty tired. Good night!

Here, you can read about the origin of this idiom: The meaning and origin of the expression: Hit the hay