be lost in something

be lost in (something)

To be fully and deeply engrossed in something, such as a thought or idea, often to such a degree as to be unaware of or insensitive to the outside world. It's no use trying to talk to Helen when she's lost in thought like that; it's as if we don't even exist! I've been lost in this show all day and didn't even hear the phone ring when you called.
See also: lost

be ˈlost in something

be giving all your attention to something so that you do not notice what is happening around you: to be lost in thought/admiration
See also: lost, something