I'm not sure if it's the same for you, but I find that if I'm avoiding talking about something (particularly in therapy), that will lead to a panic attack (it can be a sign to me that I'm avoiding something). If I let out what I want to talk about, that can ease it. I also find sometimes that if I'm panicking, letting myself cry can stop it.

If I'm really struggling to talk about it, I'll send an email in advance (either sharing what I want to say in session or, on occasion, that I want to talk about x topic but am afraid to, so could use some help doing so) or I'll have something typed out to hand him at the start of session.

In your case, with using the journals, that could be a way to share the thoughts without having to say them out loud.

Is something like walking outside an option for you with your therapist? That helped me a few times in the past with ex-MC. With walking, you don't have to look directly at each other, so it can be easier to talk, plus the fresh air. Or just sitting on a bench or something like that. Or, if he has a couch, both sitting on the couch maybe (or chairs that are next to each other, say).

For me, something cold to drink also helps if I'm really anxious.