to be so lost in thought that you don't notice what's happening around you
When I heard the news, I was in a dream, not really paying attention to anything else.
그 소식을 들었을 때, 나는 꿈속에 있는 것 같아서 다른 어떤 것에도 정말로 주의를 기울이지 않았습니다.