Switching in therapy, for me, means that I have parts that (a) want to be heard; (b) have decided my T is a potential trustworthy ally to help with that part's issues; and (c) feel that I'm not communicating their side of things effectively (which is oftentimes because I just don't know).
It calmed down for me when I got better at internal communication, which like anything, just took practice. Very regularly in therapy, when my T asks a question, I stop and listen to what different parts have to say about T's question. Sometimes those are really quite long silences while I have an internal dialogue. That works only so long as I continue to represent the whole of me in a fair way.
And that's the struggle, right? These foreign personalities that we weren't even necessarily aware of till therapy now want to participate in my life, and my therapy, and say things that are completely opposite to how I feel.
I think that getting a working, collaborative approach with my parts, which took a long time with a few of them, was essential not just to therapy being more productive, but also really understanding on that celluar level that all of these parts are me. So, if I say "that doesn't upset me and isn't a problem", when it's a huge problem for one of my parts? I was wrong: it is a problem for me, I just haven't been communicating with all of me to realise.
That all sounds very nice. But for me, there was definitely a 'crisis' period when a couple of my parts became self aware, and aware they could take over in therapy, before I'd established a working relationship with them. I was at all out war with one of my parts for quite a long time, and our relationship is still delicate.
For about a year (? not great memory of the period!) I used to wander around saying "I'm completely mad". Because that's how it felt. I was a legit basketcase, textbook mad person, switching like crazy and behaving accordingly. The understanding that "these parts are all me, and I'm not complete without them" really only developed as I worked through those internal fights and found a way to work reasonably coherently with my parts.
Like all stages of healing, it's a process. Your parts presenting openly in therapy means you're further along the process than you were previously. And that in itself, as rough as it is? Is testament to the hard work you've been doing.
Hope something in there is helpful.