in a world of your own
US /ɪn ə wɜrld əv jʊər oʊn/
UK /ɪn ə wɜrld əv jʊər oʊn/

1.
自分の世界にいる, 空想にふける
living in your own thoughts and imagination, often unaware of what is happening around you
:
•
She's often in a world of her own, dreaming about her next novel.
彼女はよく自分の世界にいて、次の小説について夢見ている。
•
He was so deep in a world of his own that he didn't hear me call his name.
彼は自分の世界に深く入り込んでいて、私が名前を呼ぶのが聞こえなかった。