Problem:

Well, most of us have experienced the wonderful feeling of the dreaded hangover. How does it work exactly? I imagine it has something to do with dehydration but what are the underlying mechanisms?

Extra points for explaining why mixing drinks makes it worse and why (or if) a hair of the dog (another drink) the next day can help. Someone once told me that hangovers are the first symptoms of withdrawal and if you drink (anecdotal evidence suggests that it should be the same drink as the night before, but I doubt this is true) a small amount of alcohol, the symptoms are alleviated. I don't really see how that can be true. Please give your suggestions on this.