I'll take a guess. When I took PT, I paid a lot of attention to what made me wonky. My eyes are the key to my balancing. With my eyes closed, I can barely walk without loosing my balance. If I walk the dog late at night, I wander all over the street, super-wonky. During the day, no problem. Have to pee at night, get out the flash light or I'll fall down or trip over myself. Driving was impossible right after surgery, because my eyes were being used to balance, not to view things. If I turned my head left and right at a stop sign, I might not see a car, because my eyes were looking for horizontal lines to balance.
Here is my guess. At home you are in front of a small screen, and your eyes are balancing you while you view the screen. You can see the horizontal lines of the TV, and other items in the room...no problem. Go to the big screen and all you can view is this big moving picture, with nothing to balance you. Maybe you gritted your teeth while you were watching. It's like when the shark is going to eat the kid during the movie, and you grip the chair arms. When the movie is over, your jaw pain is gone, you are locating horizontal lines to balance, and you start feeling better.
Try this. Close your eyes and stand on one foot, then try it with your eyes open. With some help, close your eyes and walk 20', turn around and walk back to the beginning. Walk with your eyes open. Turn your head to the left and then the right and keep your arms tight against your side. Go into a large closet, close the door and block all the light at the bottom of the door.
I'll bet you grit your teeth when you do this.
James