I don't think my own problem has reached the extent of yours but I still think I get this. Anytime I go to a function at a large place with a huge crowd I am panicked and scoping out every possible avenue of escape. I choose seats in the back and on the aisle in case I need to leave early. IKEA is difficult as you can't get out the way you go in and the exit isn't obvious (ironic that I worked there for years).

It helps me to go to places with someone else. It helps to tell them my escape plans. It helps to formulate excuses to leave early in advance. I have a CBT worksheet on catastrophic thinking that is very useful to complete before I get into such situations. It is really helpful in figuring out a plan of action should the worst case scenario arise. But it is most helpful in realizing that scenario isn't very likely to happen.