I have not had your experience, which sounds very painful. I have terminated a therapist for reasons quite different from what you have had happen, and I did have a very painful experience about it due to attachment issues. At the time I was not as aware as I am now of how powerful early attachment issues can be especially in therapy. I did feel like I was in drug withdrawal as you describe it even though I knew that I had made the right decision to stop working with him. I felt a range of things, betrayal and loss as primary. Luckily my new therapist formed a strong bond early and was very relationally focused. That helped enormously. I didn't process the old relationship since the two are colleagues and there was actually nothing problematic necessarily about the former therapist.

Now I know more about attachment and about the very powerful effects of attachment trauma. Activating that can be huge. And can potentially lead to massive affective dysregulation and other difficulties. I don't know if that is happening with you, but if it is, attending to yourself is really important and going over what the other person did probably gets in the way of that. One way to return to baseline is having someone come in who can help you feel more regulated. Sometimes it takes another attachment figure to step in.