There's a bit of a hump you get over, though. I've been recently doing some long franchise-wide marathons and once I got into the groove it was surprisingly nostalgic. It recaptured that feeling of coming back from school and just playing games until I got called for dinner.
I do understand that when I lose that flow I REALLY lose that flow. Not sure if it's age or distractions or what. All I'm saying is you can get it back and it does feel good when you manage it.