Thanks for your reply!
There's no way for me to contact my physio, although I could call his co-worker.
I don't think it can be a reaction to the last treatment, because I was better for a few days after it. I rested all week, as he'd told me to. Then, this weekend, I drove for 20 minutes to a meeting I couldn't avoid. Since then it's been hell.
The new aspect to it is the other rib/chest thing, which my physio did treat at my last session - that's how I know about it. It was the first time I'd had that problem - previously it's only been the first rib. He did seem quite concerned this time and really rammed home that I need to rest and not spend long hours at the computer.
I'm guessing that it's thoracic outlet syndrome, with another rib thrown in as well, and he's trying to halt its progress.
With it suddenly worsening this much, and him being away this week, I just don't know who to ask for advice as to what to do and what not to do. The only time I'm sure I'm not making it any worse is when I'm out walking. It's hard to rest when I can only sit bolt upright and even then it hurts, and I'm desperately trying to get used to sleeping on my back.
I'll lay off the heat pack for now and maybe try ice.
I'll also call my doctor in the morning.
Thanks again, and please do let me know if you have any other suggestions or advice.