You need rest vs You need a rest

Literally as above, I encountered those sentences in my reading.
I wonder about difference between them.

Is ‘You need a rest’ a more emphatic suggestion than ‘You need rest’ in spoken English? As I read those sentences in the book it sounds almost no difference in a general meaning.

is there any difference in nuances (or nuance?) between them?
[nuances vs nuance is complicated for me as well.]