Well this post brings back some memories.
I remember once agreeing to go away with some friends to the beach for a couple of days thinking I'd be fine. I was with people I knew and trusted, I had my dog with me, I was in my car and I could leave whenever I wanted.
I drove for 6 hours and just as we reached our destination I realised how far I had gone. I phoned my mother and asked her to call me a helicopter... seriously.
Of course she didn't she just talked to me until I calmed down a bit and then I talked to me friends and we didn't continue any further until I was ready.
It took about an hour before we could set off again, but everyone was fine with it, we were in no rush and in a nice spot. Once i got over the initial panic attack and felt comfortable again, I had a great time. I didnt have any more anxiety for the remaining time away.
This is an extreme example, but I've had trouble even going places within my comfort zone if I thought it would be hard to get out... like stadiums full of people or any place where a large crowd gathered really. I would think "what if we all want to leave at the same time?!"
Everybody is different, but I can honestly say that for me, facing this one was the best thing I did for this source of anxiety.
It was awful sometimes, but the more I did it, the less it affected me.
If I knew I was going somewhere I was unsure about, I would tell whoever I was going with that i might need their help. I learned that if I found myself in this situation (e.g a large stadium) to ask the person with me to just chat, keep it light, talk about the show we were about to see, or what the weather has been doing. I tried to draw my focus away from what was causing my anxiety. Sure enough the palpitations would subside and I would be come more comfortable. There were other things i learned that helped me, I encourage you to learn what comforts you in these times and use them as a tool to confront it.
Take small steps towards facing this trigger for your anxiety.