Basically, avoid using your computer or iphone at all costs. It freaked me out the first Sunday - what am I going to do to entertain myself? Obviously you can just read books. Or if you feel the need to work on your project you can draw your UI plans with pen and paper - but whatever you do, as long as you’re away from the computer, it’s guaranteed to be a good day, and you’ll come back extra charged up for Monday.
Anyway - so here’s to being unavailable on Sundays and spending it with friends, or with your mountain bike, or working on the garden, maybe jamming in the back yard with some guitars and a drumkit.