Yes, it is an older idiom meaning go to bed. Hit the sack is more commonly used (US)
November 15, 2019
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Neither is super common, but they're both used. I wouldn't think anything odd of it if you said that you were going to hit the hay or hit the sack, as the other commenter mentioned. It's definitely very informal though.
November 15, 2019
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Chinese (Mandarin), Chinese (Hakka), Chinese (Taiwanese), English, Russian, Tibetan