GP appointment next week. Do I mention it or not?

I have an appointment about something completely unrelated, lower back, nothing to do with any of this. But it occurred to me that there might be an examination and I have no idea whether I am supposed to bring it up beforehand or just let it be a surprise for both of us.

I would rather not have the conversation at all. I would also rather not have a GP discover it mid-appointment and have to improvise.

What do people actually do here?