Drink a large glass (or two, or
three) of room temperature water. I'd suggest drinking one glass and then drinking another, slowly.
If you are feeling especially dehydrated (also, if you are on a low-sodium, low-mineral diet) try some pedialite or off-brand of the same variety - it's what you give children who are
throwing up or otherwise losing fluids quickly and I drink it when I'm sick or feeling especially dry. It will help with your issue.