This sounds suspiciously like IAPT that you're describing, do you know if it is?
IAPT is notorious for setting people up with harsh tripping points for immediate discharge for the service, and is accessed on a self referring basis.
If it is, it's not really likely to have a transformative impact on anything other than mild and straightforward problems. It tends to be quite basic - completing worksheets - without much basis to dig deeper.
However, plenty of the therapists working within the service are good and will be able to help get you started, give you a direction to aim towards, and work out key areas to target.
I had to start off with IAPT before I could get access to any other kind of service. The things I learnt there, and the experience of trusting the therapist, laid the foundation for the more difficult work I did later elsewhere.
Any form of therapy can initially be destabilising. But you do have to remember that after that initial period comes improvement. I tend to think of it as having to leap through the edge of flames to escape a burning building - tough and scary, but necessary and temporary to get somewhere safer and better.
But I can understand your apprehension. It really worried me. I think it gets talked up a bit sometimes to make sure people are aware and it doesn't take them by surprise. It won't necessarily be a bad as you're worrying. And it will only be temporary. They also provide support with coping mechanisms.
Three is another thread running at the moment about whether psychological therapy is useful for chronic pain. You might find some of that helpful /relevant to your circumstances? It has "am I being palmed off?" in the title.
Most if not all therapies for anxiety will involve you sharing your thought process and feelings with a therapist. So it is something you need to feel ready to work towards. They won't expect you to pour out anything on day one.
It won't be an interrogation. You'll be asked what you feel able to share. They'll also provide tools for you to think things through on your own at home, and then you could come back and ask questions on anything extra that came up, for example.
It might be worth thinking about whether it would be helpful to view it as the start of a process of facing your anxiety about working with a therapist?
Unfortunately, the way mental health services are set up and funded right now it can be a bit game playey, where you have to show you've taken up what is offered, worked at it, yet are still struggling before anyone will consider alternative services. That's why it has the "48 hour notice or you'll be discharged" rule written in, to get people off the books at the earliest opportunity.
I do not remotely agree with it, I think it's wrong, but I'm just giving you the heads up.