I don't like being confined anywhere like this. It's a social confinement though. Like...if you got up and ran off screaming they'd think you were nuts but you really really really want to jump up and run off screaming because you're trapped but you're not really trapped but you feel trapped!!!!!
Oh my, been there, done that. I am much better now. Recognizing your triggers and accepting that you feel insecure in those situations will help your brain to calm down. A LOT!
I still can't go sit in the choir loft at church unless I am sitting beside the exit. I still can't go sit at the front of a classroom unless it's right by the door. I don't do it. I go early to new places to I can scope out the lay of the rooms and pick my safe zone. I sit by the exit at the theater. I sit by the exit every single place I go. No joking. If I have to ride an elevator I tell my husband to tell my some funny jokes or show me cat/dog pictures on his phone from some web site. Anything to distract me so I don't have to think about where I am or to look around at the walls.
It works. I drive back streets sometimes too. I don't drive on the highway, I take main streets through town, I go 35-40 instead of 65-75, I recognize I feel safer if I use my avoidance behaviors. As long as they work for you there isn't any reason to not use them.
Plan ahead. Close your eyes and use visualization. You're sitting in the chair. What would happen if you suddenly needed to run to the bathroom and have diarrhea or puke from food poisoning. They'd simply move out of your way. IF you need to get up and move around tell them you are getting cramps in your legs/back/and need to get up for a few minutes. They'll simply move out of your way.
Practice visualizing that you are not trapped socially or physically and take deep relaxing breaths. Push your shoulders down away from your ear lobes where the tension has them so tightly strung up. You can do this. Breathing and relaxation and visualizing a good outcome will help you get through this.