I have never hears any therapist encourage dissociation. It's common in trauma survivors, but it's not an adaptive response once you're no longer being traumatized. They tend to want to focus on grounding skills and on discovering and dealing with the trigger(s) that cause the dissociation.

What's most helpful to me when I'm dissociating is if the person I'm with can get me to talk and move, even if it's just a little bit at first. A lot of people find that strong sensory stimuli (ice, strong scents, strong tastes, etc.) help them ground, but I find that those often cause sensory overload that worsens my dissociation. For me it's all about getting unfrozen and reassuring me that I'm safe. It sounds goofy, but I find reciting things helps--poems I've memorized or even goofy little ditties. (The therapist I worked with on a trauma unit was particularly entertained by one I learned as a theater warm-up, Jerry Lewis's announcer's test.) Moving my fingers and toes helps, and if I can manage to shift my position, that helps even more.

It's kind of a trial and error process to find what works for you, but a good therapist should be able to help.

I often felt embarrassed/ashamed when I dissociated in therapy, but it helped a little to realize that it's actually a pretty common thing for trauma survivors, and it helped when the therapists didn't freak out and act like it was something awful and scary. And it gets easier to manage as you learn skills to deal with it and as you work through your trauma stuff.