I did it for 9 months and it made a REMARKABLE difference in my recovery. There were times when different therapy exercises might cause a flare in symptoms, but I would lay down flat on the floor until it passed, normally a few minutes.
When I started, I couldn't ride in a car without getting disoriented and sick. I couldn't do anything where I wasn't standing directly upright, or I would feel dizzy and have to lay down to make the room stop spinning. It was really awful. Even simple things, like watching hockey or football, (which was a HUGE part of my down time before my accident), made me sick.
It took me 9 months to graduate, but now I am able to watch sports, ride in a car, drive a car and only very rarely have moments where I feel "off". Not so much nauseous or dizzy, but off.
For me it was totally worth it. I HIGHLY recommend it. The first few sessions are rough. But, what you are doing is training your vestibular system to tolerate increasing levels of movement and sensory information. So it's like when you start to exercise. The first few times are rough on your body, but over time you continue to build endurance and strength. Same idea here. However, you therapist will tell you what is a good level to strive for, without overdoing it, (making yourself feel worse or causing your symptoms to flare for hours afterwards, etc.)
If you have any specific questions, feel free to ask