Re buying those tickets - I would, and see how I feel when I get to that date, even if you lose the money. If you feel like going you will at least know that you are a bit better, if you don't, you will know that something isn't working.
Was it someone on here who said that anxiety is when you worry too much, depression is when you don't care about anything at all? I was depressed a long time ago but it was a lightbulb moment when I read that. I'm so scared of it happening again that I do have some very elderly pills squirrelled away, as a sort of comfort blanket.
I have arrhythmia too, and no-one ever mentioned it being a problem 20-odd years ago. I am still alive to tell the tale!