A hangover is the after-effect following the consumption of large amounts of one drug or another. In particular, it is most commonly associated with the consumption of alcohol. For other addictive drugs, the correct terminology is withdrawal, which is a hangover of sorts for that particular drug.
The Alcoholic Hangover
Different alcoholic drinks are reputed to have different results in regards to the strength and duration of the hangover associated with them. Dark drinks (red wine, stouts) are reputed to give particularly awful hangovers. It has also been suggested that the more expensive the drink the less of a hangover it gives. This is widely thought to be propaganda distributed by the rich. Others may suggest that more expensive drinks have less harmful additives. An expensive wine, for example, does not need to have additives to reduce its sharpness, as it will have been made such that the natural taste is palatable. Getting drunk on good champagne, whilst expensive, produces a much reduced hangover.
An alcohol hangover is associated with variety of symptoms, including dry mouth, headaches, bloodshot eyes, nausea and vomiting, and sensitivity to light and noise.
Hangovers are multi-causal. Alcohol is an enuretic resulting in dehydration, which causes headaches, dry mouth, and lethargy. The large amount of fluid passing through the kidneys also results in a loss of blood sugar, and other water soluble vitamins and minerals. The loss of vitamins and minerals impairs the body's ability to perform basic functions internally, such as toxin removal, hence the achy feeling. Alcohol is also a metabolic poison, and its impact on the stomach lining probably accounts for the nausea. Finally there are various nervous effects. The removal of the depressive effects of alcohol in the brain probably account for the light and noise sensitivity. It is also thought that the presence of methanol mixed with the common ethyl-alcohol that exaggerates many of the symptoms, which probably accounts for the association with dark drinks. The amount of tannin in the drink may also have an effect.
The amount of flavour compounds in the drink will increase the hangover, so a dark beer, or stout, such as Guinness will produce a worse hangover than drinking the equivalent amount of alcohol diluted in water (basically Vodka).
Hangovers are really unpleasant, and are normally associated with statements such as "I wish I were dead" and "I am never drinking again". The former is almost universal true, and the latter almost universally untrue. Common folk medicine has a wide variety of hangover cures. Indeed there appear to be nearly as many ways of curing hangovers as there are of getting drunk in the first place. Almost all of these hangover cures have one major thing in common, which is that they are no where near as effective at curing a hangover as alcoholic drinks are at getting you drunk.