Oh wow, that sure is a lot for being sudden. I'm not to sure, but I would go to a doctor and ask because that sounds pretty serious..
It could also be a sudden dramatic drop in blood sugar.
I can tell you, I feel this so often. It's called Panic Disorder. Some people don't know they have this common form of anxiety but when it strikes, it's alarming; especially if you've never experienced it before. The sweating, stomach pain, fainting and breathlessness is all relative to panic attacks. You should look into it a little more...