I've heard a lot of anecdotal evidence about champagne affecting some people that way. Many times any liquor can cause mild dehydration and some mild toxicity...however 2 glasses isn't the amount that is often cited.
Out of curiosity, do you have any such issues if you had 2 glasses of wine instead? My guess is that it's also true for wine..that reaction. If that is the case, it could be that it's the sulfites in the wine and champagne to which you're reacting.
PS. As I've read your comments over a period of time I know this about you and I can't imagine you'd have drunk cheap