Hmm. If I'm calling it the wrong thing, then, maybe I should give an example of me enjoying nerding out to see what I should be calling it.

If I were to step back and think "It doesn't actually matter what the specific stats are for human versions of My Little Pony Characters in a D&D 3.5 setting, no one is going to be judging this for accuracy." then I'm not actually having fun while making their character sheets, and I wouldn't have bothered.

But If I'm just making the character sheets, then it is fun, and I'm just enjoying on nerding out on something incredibly esoteric. And then, my wife joined in while I was attempting to consider Applejack's bonus feats, and she wanted to make a 7th character so she could participate, so we looked up the name of that one human friend that hung out with the my little pony characters in an earlier show. (Megan) and then we pulled out more D&D books and she came up with neat campaign ideas.

And then I realized we had spent hours together working on this idea and the time just zipped by because we were intently focused on enjoying a nerdy activity together.

It seems like a flow state to me, but I would not be surprised if I should either call it something else or if your experience with evacuation plans just felt entirely different.