My old psych said I had agoraphobia. Though when I say that to people they assume it means that I can't go outside
but that's not what it is, I am terrified of any situration where I cannot escape or when escape would be embarassing. So for example I cannot cope with crowds, I cannot go on busses as if someone sits next to be I feel trapped and unable to get off the bus until after they do (so missing my stop), I can't cross bridges either as I know that once on there is no way off if something goes wrong.
I have a sort of "safe zone" within which I can walk about and function freely, but if I step beyond that then it's a bit like when you walk up some stairs and think that there is one more step than there is, and your foot just falls through thin air as your stomach jumps. The problem is the edge of this "safe zone" seemingly can alter with no warning, on some days I can freely go anywhere, on others I cannot leave my room.
I can't do queues either, like you I panic and fear that I may pass out, or that I am being too slow and annoying the people behind me, or just that everyone else deserves to ge tto the tills before me so I shouldn't be queueing anyway. I can't use non-self service checkouts as I jut panic so much that half the time I leave the queue before getting to the front, for some reason the self service queues are easier though (no idea why)
I've been put on medication for anxiety which has helped imensly. Sipping water helps a little too, I think though that is because as the panic starts you start to feel more and more warm until the heat is just unbearable and suffocating, and I think maybe sipping water helps to prevent that a little