haha if they see you looking like that they will....this is why people UNDER 21 should NOT drink....anyway i think you might want to sober up b4 you go downstairs...like try water again...ur severly dehidrated for a reason.
Under 21 is only in the US. I'd say people under 16-17, although I think children need to be brought up with alcohol so they don't go wild with it when they reach that "magical age" (whatever age that may be, in whatever country they're in!).
Anyway, you've lost valuable minerals and vitamins. Eat lots of fruit, drink a lot of water and take some painkillers. Unfortunately, there's no "magical" method to cure it all, just ways to alleviate and take the edge off the symptoms a bit.
And in future, if you're gonna drink that much, make sure you drink plenty of water before going to sleep/before getting in, as this can take the edge MASSIVELY off of a hangover, and even prevent it!
GOGO shower - Brush teeth - Eat.
You will feel better.
As for your parents, just be normal, they may not even have noticed, and if they did they would bring it up anyway.