Similarly, if I've been deeply focused, my brain has switched out normal, every day concerns for work material, my brain state is settled in to focus mode, etc. I spend hours a day (and have for years) teaching myself to focus on a large, abstract set of information in a particular state to attack problems. (It's actually a lot like visualization meditation -- to be able to hold a complex model of what you're working on in your head while you work.)
Im not able to instantly turn it off, it takes time to switch out of that mode of thinking and to bring back the "normal" information. It has nothing to do with priorities -- context switching, particularly a mode switch, takes time.
My ex used to hate that, she'd say "your not listening?" and I'd repeat verbatim everything she said and then she'd get annoyed because listening and listening are different things.
Current GF gets into a flow state herself so she is way more understanding :).
Happens to me all the time :)
I feel like it's physically painful for me to not work in this way. I can not give undivided attention when there's something that needs to get out, and am certainly jealous of people who can context switch out of a flow like it's nothing.