The word 睡觉 is a verb-object, which means you can split it apart and use it in some of Chinese's more complicated grammar structures. The basics of it are that the first character 睡 is the verb "to sleep" which the second character 觉 is the noun "sleep." Literally, this word means “to sleep a sleep." In common usage, these characters generally stay together unless you are adding a modifier, so think of them as one word!

睡 is verb, 觉 is noun. 睡觉，together is a verb. 我睡了一个觉，觉 is a noun in this sentence and it means from the moment you slept to the moment you woke up. Eg. 午觉，一觉醒来 Hope you understand.

”觉“有两个发音，jiao，四声，才是”睡觉“的意思。”觉“是指”从睡着到睡醒“整个过程称作"一觉“，所以可以说，我睡了一觉。还可以组成”午觉“，”睡觉“，总的来说，”觉“很少单独使用。而”睡“是可以单独用的，不一定要组合成”睡觉“，”你睡不睡一会儿？“睡！”。绝对不能说成“你睡觉不睡觉一会儿”。

thats a good question ~~ exactly 睡觉 means sleep，generally speaking we put them together to express sleep ,instead of dividing them 睡觉 is a verb as well as a noun ~~ example: 1 I want to 睡觉 (verb) 2 睡觉 is good for my physical health (noun) I hope that you understand my explain.

I just want to understand why you have been thinking in this way. There are amount of similar cases like 跑/跑路， 爬/爬山，醒/悟/醒悟，etc. Maybe in Russian this type of vocabularies is not existed?