Nanc, I hope you're feeling ok now, scary stuff...
I had to just let you know that my mum has had exactly the same symptoms quite a few times over the last five years or so, and still hasn't worked out exactly why. She has been to ER a few times with it, it looks really frightening at the time, and makes her feel really poorly, and then tired and wobbly for about 24-48 hours after. She has to take a kind of mega-anti-allergen tablet that she calls a 'bomb' - makes her sleep for a day, and then she feels a bit better. The docs have checked out all sorts of things like laundry detergent changing, a plant she might have brushed against, new clothes, different food etc, but nothing has been conclusive. Her best guess is a plant in her garden that she is allergic to, and she wears gloves now - it does happen less often now.
Hopefully you and your docs will be able to track down what caused it - I hope they offer you an allergen test (although not one that involves using pin pricks on your arms obviously

).
Take it gently for a few days and I hope this is a one-off thing!
Bram