Knees.

My knees are killing me.  I'm not exactly sure why, but they got bad on Saturday (when I was dancing, but not excessively so) and I can barely walk at present.  I can cycle to some extent (uses different muscles and isn't weight bearing) but standing is very painful.

And it's the Quayside Cloggies 25th anniversary tour/party this weekend.  Unless things improve, I'm going to have to miss it.