Well folks how right you all were!
I was so very worried about getting through the day and it was no bother, repeat, no bother at all. The mild discomfort lasted a whole 5 seconds, the screen was fascinating to watch and I was given the result on the spot. And it was the best possible - all arteries are clear so I don't need bypass surgery, just 2 valves to be sorted! Yaaayy!!
Downside - the cheese sandwich was rubbish.
Thank you all so much for helping so much these last few days, unbelievably appreciated by the CEO of The Wimp Club although I think I might resign my membership now.