That sounds like a very, very difficult place to be. It is as though this angry version of yourself who feels completely worthless is in a battle with your rational self. Somehow his version of you takes over the session and prevents you from communicating with your therapist. It sounds incredibly frustrating.
I'm not sure you should be trying to drag yourself out of this state. It sounds as though those children really do need to be heard and accepted rather than fought against. If you don't allow the young feelings to be heard, I wonder if this would have echoes of your childhood for you? Were your feelings accepted or stifled by your caregivers? Perhaps now is the time to let those child states have their say so they can be integrated and accepted as part of you.
Would it be possible to explain this to your therapist in an email and devise a plan for working with the feelings in session? You could ask him not to raise the email in session and tell him why. It sounds like your adult self and your therapist need to get your heads together and work out how best to give these feelings space and acceptance.
It's tough work and it sounds like you're right in the midst of it