na-adjective, noun which may take the genitive case particle 'no', noun
absorbed in; crazy about; devoted to
The most common modern use. Often appears as 〜に夢中だ or 〜に夢中になる for being very interested in something, or 夢中で for doing something with full attention.
彼は新しいゲームに夢中だ。
He is crazy about the new game.
子どもたちは虫取りに夢中になっている。
The children are absorbed in catching insects.
noun, na-adjective
forgetting oneself; trance; daze; delirium
Describes a state of losing ordinary self-awareness through panic, excitement, pain, ecstasy, or confusion. In everyday Japanese, this often appears in phrases like 夢中で or 無我夢中で, meaning one acts without thinking clearly.
火事だと聞いて、夢中で外へ飛び出した。
When I heard there was a fire, I rushed outside without thinking.
彼女は夢中で助けを呼んだ。
She called for help frantically.
noun
within a dream; while dreaming
Literal use meaning “inside a dream” or “while dreaming.” In modern everyday Japanese, 夢の中 is much more usual; this sense of 夢中 is literary or old-fashioned.
古い文では、「夢中に故郷を見る」のように、夢中が「夢の中」を表すことがある。
In old writing, 夢中 can mean “in a dream,” as in “to see one's hometown in a dream.”