Is this ~んだ form an explanation?

Question

I know the んだ form is used to give and ask for explanations, but I'm not sure about its usage in this passage; context: a girl asked a boy how much he loves her, he answer and then starts explaining his answer:

そして僕は突然、自分が知っている誰からも、自分が知っているどこの場所からも、信じられないくらい遠く隔てられ、引き離されているんだと感じる

It seems like an explanatory usage of んだ and it makes sense, since he is giving an explanation; I'm not sure because that sentence is just part of the explanation the boy gives, and before and after んだ is used just another time (in a なんだ form). So I was wondering: why that sentence uses んだ, while the rest of the explanation doesn't? It's like the character felt the need to stress that part?

For reference, some more of the explanation (if needed I can copy also the following part):

ある時、夜中にふと目が覚める。正確な時刻はわからない。たぶん二時か三時か、そんなものだと思う。でも何時かというのはそれほど重要なことじゃない。とにかくそれは真夜中で僕はまったくのひとりぼっちで、まわりにはだれもいない。いいかい想像してみてほしい。あたりは真っ暗で、何も見えない。物音ひとつ聞こえない。時計の針が時を刻む音だって聞こえない―時計はとまってしまったかもしれないな。そして僕は突然、自分が知っている誰からも、自分が知っているどこの場所からも、信じられないくらい遠く隔てられ、引き離されているんだと感じる

Answer 1

Yes, this んだ is an explanatory-の followed by だ.

In this paragraph, the weird situation that needs to be explained is 誰もいない, 何も見えない, 物音ひとつ聞こえない, etc. In other words, these are treated as "questions" rather than explanations. And the corresponding "explanation" (or "answer") he suddenly noticed is "僕は誰からも、どこの場所からも引き離されている".

• 何も見えない。 物音ひとつ聞こえない。
  → I can see or hear nothing. (Why?)
• そして僕は突然遠く引き離されているんだと感じる
  → I suddenly noticed I'm separated from everything I know! (And that's why I can see or hear nothing!)

By the way, is this whole thing really an answer to "How much do you love me"? Then you can forget that context for now. Obviously, saying 引き離されているんだ does not serve as an explanation to her question. He has started a long story which seemingly has nothing to do with their love.