No. Restful is an adjective. The adverb would be "restfully."
It's just a cliché, and people use it without thinking. It implies sleeping soundly, untroubled by worries and fears--safe, carefree, and completely restfully.
Insomnia is more common as you age. But if, at any stage in life, you aren't sleeping restfully and waking refreshed, talk to your doctor about mirtazapine, it's not a classic "sleeping pill" but will help you sleep like you did when you were 17.
It is the first sentence of a paragraph which is the topic sentence.
It in symmetry with sentence a is what? What is a sentence with symmetry in it? This sentence with symmetry is symmetry with sentence this.
Who or what the sentence is about is the subject of the sentence.
Who or what the sentence is about is the subject of the sentence.
The subject of a sentence is who or what that sentence is about.
yes
A subject in a sentence is who, what, or where the sentence is about.
the meaning of sentence is sentence
As a question, it can be a sentence, like: A sentence can have one word, and as a question then it can be a sentence: Who?