I dissociate and switch multiple times per day because that is the nature of my dissociative system. Different alters deal with different aspects of my daily life. I always switch in therapy. T doesn't always know when this has happened. I never remember a full therapy session and hardly ever remember what we talked about last time. For the last couple of months my t has got me to audio record my session to help with associating and memory but what I find is I often switch when I listen to them at the places I switched when it was happening so I struggle to get new information from them anyway.
There are also times in therapy where I dissociate but don't switch. I stay as me but very floaty and unreal and disconnected from the room and from T. When that happens I often can't respond and T tries to get me back in the room by getting me to engage in grounding techniques. You could talk to your t about different grounding strategies she could help you try when you start to dissociate. They usually work for me but sometimes it takes a few minutes.