It's Sunday and if you are anything like me you like to have the odd Sunday when you do absolutely nothing.
As an introvert don't think that you have to organise something because you don't. Don't feel pressure to make something up on Monday morning about how your weekend was. If you didn't do anything say it with pride because you know yourself and you know for you to get the most out of your week, you need your rest and solitude.
If you need the weekend or even just the Sunday to recharge then do it and don't feel guilty about it.