Any language. How can someone lose someone else's atttention. It's something internal.
He is losing her mind. Also would be a strange sentence. It doesn't make sense.
Have you ever tried to get someone's attention? And then keep it? Well this person is not succeeding.
I'm fine with the sentence but I have a problem with a vowel. And the construct for "attention" under the מ should it not be a segol? He says it as a patakh.
I agree with airelibre here. This is something that teachers say about lectures, but I imagine stand-up comedians, priests giving sermons, and others who are trying to hold the attention of a crowd probably use it to. I might look at a written lecture and point out "here is where you lost their attention."