The closest I've came to a v* with no warning senario was about an hour from feeling yuck, to the time of v*.
This is very fast, at least from what I know. The only times I have ever had that truely happen, is when I was preganant, and even then I had a good minute or two before the actual v*ing started!
Hope this helps.
Crystal
PS...My aunt/best friend and her fiancee, and her three kids all had norovirus two weeks ago. They felt like crap for a good 6 hours before anything "happened", and they actually only v*ed 1-3 times. Not as drastic as they put in the papers, huh?
That, which does not kill us, makes us stronger!