The ZAMM reference is spot on to me. The moment I used to get an interruption (typically an incoming call, but not only that), what happened to me was just what Pirsig describe of the gumption leaving you like air from a baloon, psssst.

I eventually got into 'the zone' and I was actually quite good at figuring out problems with little context, but my gumption was gone nevertheless, and I was useless for whatever thing I was working on before the interruption for mostly the rest of the day.