It is not physically possible to get a concussion from vestibular physical therapy exercises (it requires that physical stretching of the nerve cells in the brain, remember? )

It IS possible to trigger a migraine attack (which is more likely the source of your current living hell than a new concussion) from vestibular physical therapy exercises (this actually did happen to me once because of a PT who didn't actually understand my condition), but correct PT is all about controlled exposure. So you would only be doing exercises to elicit very slight amounts of discomfort in order to train the brain to "turn down the gain" on your sensory inputs. Doing proper PT you would be nowhere near the sensory overload needed to trigger a new migraine attack.

Please don't give up. I know you feel like you're in hell. Trust me--I've been there. If you have what I have the attacks are so miserable that you just dread even being awake. The dizziness, the nausea, the fatigue, etc. BUT please know that these symptoms resolve. They are reversible. There are treatments. This is temporary. There is a life worth living on the other side of this.