Using のうちに to construct an adverb

Question

For the full text see here. The fourth line from the bottom of the linked text is:

イヤリングをつけ終わると、無意識のうちに、ドアの耳に口をよせた。
When he'd finished attaching the earring he unconsciously put his mouth to the door's ear.

I don't understand 無意識のうちに. I assume it means "unconsciously". But isn't 無意識 a na-adjective that means unconscious? Why can't I just use 無意識に?

I would have read 無意識のうちに literally as "while unconscious", but I'm quite certain that is the wrong interpretation.

What is going on here?

Edit: Thanks for the comments so far, but they are missing the point. I believe that subconsciously, unconsciously and unawaredly (if that's a word) all have similar meaning. I'm not confused about the person being able to do something while his brain is shut down. The main focus of my question is on why のうちに is used instead of just に and whether this is a grammar point that applies more generally.

Answer 1

I don't understand 無意識のうちに. I assume it means "unconsciously". But isn't 無意識 a na-adjective that means unconscious? Why can't I just use 無意識に?

You're right, 無意識のうちに means "unconsciously". In your example, it can be rephrased as 無意識に without changing the meaning.

As explained in this thread, the うち indicates 状況 (situation) in which an action or event takes place. According to 明鏡国語辞典:

うち【内】
🈩⑩㋔ 《「…のうちに」の形で》ある状況下で行われる意を表す。…[裡]{り}に。
「大会は成功のうちに終わる」「暗黙のうちに了解する」

プログレッシブ和英辞典 gives a few more examples:

うち【内】
➏〔ある状態の中〕
会は成功のうちに終わった
The meeting ended successfully.
拍手[喝采]{かっさい}のうちに舞台を去った
He left the stage amid loud applause.
苦悩のうちに生涯を閉じた
He died in great mental anguish. / He died with his mental suffering unrelieved.

So.. to answer to your question "...whether this is a grammar point that applies more generally", I'd say yes. Some more examples I can think of right now...

「平和のうちに解決する」
「無言のうちにその場を後にする」
「極秘のうちに進めてくれ。」
「大盛況のうちに幕を閉じました。」
「失意のうちに・・・」「混乱のうちに・・・」 etc...

_{(Some examples can be rephrased using に or で, as in 平和に解決する, 無言でその場を後にする, 極秘に進めてくれ, etc. I think using ～のうちに sounds a bit more formal/literary.)}