Apparently mowing the lawn was a very good thing!
I had to concentrate on stepping very correctly, and making the leg do its proper work, while the mower kept me balanced. Now my hip is far less stiff, and the distance I can extend that leg has increased. I did stationary biking for ten minutes afterward to prevent it from stiffening, just in case. So what if it took four times as long to mow the grass (and I didn't even get finished)?
So with my hip feeling great, off to bed!