I had my ankle rebuilt in Thailand about 12 years ago after a bad fall. The surgeon was wonderful--showing a still-groggy me pictures of the inside of my ankle and gleefully saying " It was much worse than we thought, but you have huge tendons (you really DO walk a lot!!), so with lots of wires and transplants we rebuilt it all!" They did incredible work. Since then, after loads of physio, I can walk, run, cycle...sitting seiza isn't quite so easy, but most days I don't really notice it.
But today is one of those days where something I did set it off. I can feel every bolt. So I hung around without really getting properly dressed and made some test sheets of paper with one of the kids and finally got a little further on the Overengineered Yoghurt Maker project and did maths with the kids and had Long Necessary Conversations and...as much as I hate days when I can't walk, it hasn't been a wasted day.