It means sleeping is something you like in general (i.e. an activity you enjoy).
If you want to sleep right now you can say Я хочу спать.
We do not distinguish between "like to do smth" vs. "love to do smth" the way English does. Мне нравится спать and Я люблю спать are roughly the same in strength (the latter is probably a more common wording).
If you need to express a stronger feeling of liking something, you can add "very"(e.g., очень люблю + infinitive) or use some other verb (e.g., обожаю "adore" + infinitive).