眠りに

into sleep

→ 眠り
phrase Uncommon #14,891
into sleep Usually appears in the expression 眠りに落ちる, meaning to fall asleep. The に marks the state entered: literally, “into sleep.”
JA: 椅子に座ると、すぐに眠りに落ちた。
EN: I fell asleep as soon as I sat down.

最高の眠りにつける

You can get the best sleep.

— アバウト・タイム ~愛おしい時間について~ (2013)

トムソファ眠りに落ちました

Tom fell asleep on the sofa.

彼らはときどき何年も眠りにつく

They sometimes fall asleep for years at a time.

— コーカサスの虜 (1996)

座るや否や眠りに落ちてしまった

No sooner had I sat down than I fell asleep.