Fencing again this week, after further abstinence due to work, lurgy, convalecence, and work. It started aching quickly during backsword exercises, but I managed some freeplay, and it was fine Tuesday morning, and Wednesday morning and Thursday morning. Yesterday morning, it was hurting again in the same way, and got progressively worse during the day and evening. Cue bucketloads of Ibuprofen gel. It's still a sod now.
So, the bad: it could be like this for an arbitrary amount of time.
The good: it wasn't caused by fencing this time, so probably wasn't last time, either. I suspect I'm giving myself a half-nelson while asleep.