This is the 3481st most frequent Japanese word.
睡眠
Sleep.
The word "睡眠" is used to refer to "sleep" in the sense of having adequate rest.
十分な睡眠をとることは健康にとって重要です。
Getting enough sleep is important for health.
Here, "睡眠" indicates "sleep" as an amount or duration, focusing on the quantitative aspect.
彼女は睡眠時間が短いことを気にしています。
She is concerned about her short sleep duration.
In this sentence, "睡眠" is used to describe "sleep" in relation to its quality or condition.