Thanks to all.

There is just the pain as the finger opens and closes OK. I can still play my other instruments, without any restriction. It just hurts a bit.

You get these aches and pains, from time to time and put it down to overplaying or whatever. It is unusual for me at least, to be able to identfy exactly what the cause was. Doing that is some of the way to avoid doing it again, I suppose?