I have two speeds - "asleep" and "rip off fast like a band-aid" - I don't know how to slow down. I am so open to suggestion.
Would it help to think of it not so much as slowing down but more as breaking it down into steps that you need to do in order? Maybe that could also help with the feeling that you're being held back from getting the poison out of your brain. Getting stable is the first step in getting the poison out. If you're working on getting stable, then you've started trauma work. The processing stage is a later step, and you'll be working towards it.
Getting stable is an active step. There are things to do with stability that you have to look at and talk through in therapy, skills to learn and practise, milestones you need to achieve. For example, eating three meals every day. Learning grounding techniques and practising them. Doing a relaxation exercise every day. That's something you can put your energy into at this point, and it will also move your forward in the direction you want to go.
Processing trauma in therapy isn't just talking about it. Processing is talking about it and coping with what that brings up. If you talk about it and are dissociating, or you have a meltdown because you don't have the skills to manage the inevitable reactions, then you won't have processed it.
The fact that all sorts of things about trauma are coming into your head now means it's actually the best time to learn and practise things like grounding, containment, coping skills, distraction and relaxation - and actually
not a good time to start processing. You need skills in managing the thoughts and memories so you don't get overwhelmed and don't keep dissociating so easily. Those skills can help you now, and they can help you when you're ready to start processing things. You need to use them all the time.
Maybe you and your therapist could identify what would be helpful for you, come up with a plan, set some goals and focus on that for the time being. I don't have the whole picture of course, but I imagine that he must have some intention for the chit chat about what's happening during the week, perhaps to keep you grounded by focussing on practical things. I would suggest you ask for a more directed approach to learning and practising things that will help you stabilise. If your therapist isn't willing or able to do this, then that would be the point where I'd be wondering if he was the right therapist for me.
There's a lot that you can put your energy into, in order to "slow down" on processing. You don't have to stop everything and wait for stability to descend on you. It won't anyway, you have to create it, so the sooner you can start working on that the better.
You sound frustrated you can't get to work at this point, but I think you can - you can work on getting stable.