I think going numb during therapy would be like if you're overloading your mind with too much about the trauma and so as a defense mechanism you go numb because the mind/body can't handle the stress and is trying to protect you.....basically it would indicate you're taking things too fast and need to either slow down or take a break from delving into all the trauma recovery work.

I have been feeling pretty numb myself lately, trouble is my brains really doing a good job of pushing the thoughts away and numbing me so I really don't know what's causing enough stress for the numbness to take place.