Good morning, everyone, and thank you for your comments. Chest still achey but it's not the sick ache of yesterday. I think it's probably just a rather nasty common cold virus. I get this kind of thing very often but it's not usually quite so bad. My system "deals with" the virus but, boy, does it complain about having to do so!
I think my chest joints (costal cartilages) are particularly sensitive to any kind of intrusion, probably because of the underlying (^underlying^!? Ha!) arthritis which affects more and more of me as time goes on. It has stopped my dancing, cycling and swimming over the last ten or twelve years (I know swimming should help but it doesn't). My muscles are fine but if I swim even a few lengths, I'm floored for a couple of days because of the chest ache; it must be a bone/cartilage thing. My chest tells me when the barometric pressure is rising or falling too, usually before the 'proper' barometers catch on 
My GP knows all this (well, he's been told anyway). I don't think there's anything he can do. Roll on medical research into arthritis, I say!