be miles away

To be noticeably distracted and unfocused. Of course you don't remember me saying that—you were miles away the whole time! It's the last day before Christmas break, so my students are miles away. I hope my co-workers don't notice that I'm miles away. It's so hard to not be able to tell anyone I'm pregnant yet!

be miles away

be lost in thought and so unaware of what is happening around you. informal

be ˈmiles away

(informal) be thinking deeply about something and not aware of what is happening around you: When I ask him a question in class, he just looks at me. He’s always miles away. ♢ ‘What do you think of Anne’s idea, Dan?’ ‘Sorry, I was miles away. What idea is that?’