Both my T's do this. One asks me directly "Are you dissociating". Part of this is to call my attention when it is happening, then it becomes learning for me, so I can better recognize when it is happening as well as what happens JUST before it happens. My other T just checks in to see if I am understanding or bring my attention to what happens to my connection to him when I dissociate. So I think what your T is doing is just part of the work. Of course you are the one on the receiving end and if it makes you uncomfortable it is probably a good topic for discussion in therapy.