My theory is that we ALL have primitive emotions such as anxiety and fear, but normally don't "feel" these things due to balancing factors in the cortex regions of the brain.

Primitive emotions are stored in the more primitive areas of the brain located near the center of the skull, and thus more protected from physical trauma. These raw emotions are not undesirable per se, as they conferred adaptive value to a developing species (translation: fear and anger kept us alive long enough to propagate).

In TBI, more advanced areas of the brain (i.e. closer to the surface) are damaged, wiping out more advanced cognitive processes that normally balance the primitive drives. Courage, for example, is a higher form of cognition, and balances the fear drive.

You DID have anxiety and fear of public communication before your injury, as we all do. You simple kept these feelings under such efficient control that you didn't even realize you had them. That's what they meant by "bubbling up". These feelings are literally accreting from deeper parts of the brain, with nothing to stop them.

Your brain injury robbed you of your power to control primitive emotions, and you must now find other ways to compensate. Some of the ways suggested are good- Tai chi, laughter. I have found very good benefits from martial arts type stuff, and meditation (and have some theories on that as well).