Unfortunately when it comes to drinking, a great night is usually followed up by a miserable morning. A typical article giving advice on how to cure a hangover often says "drink less," "alternate water and drinks," or "eat while or before drinking." Well if you had done all that you wouldn't be searching for a how to fix a hangover. While yes, the first step in alleviating a hangover is certainly to prevent a hangover, once you already have a hangover you don't want to know what you should have done, you want to know what you can do now!
The first step is probably the most obvious, but if you can sleep, do it! Sleeping off a hangover is one of the most effective ways of curing a hangover. So if you have the time and your head isn't pounding too much, just sleep.
The second step is as obvious as the first. A hangover is caused mainly by dehydration, so drink lots and lots of water and fluids in order to rehydrate your body. I find going to sleep with a Nalgene next to your bed or filling one as soon as you have the energy to drag yourself out of bed is the best plan. That way you don't have to keep getting up to refill the water. Fruit juices, sports drinks, and soups are also great ways to rehydrate and re-nourish your body. Fruit juices will replenish vitamins, sports drinks have electrolytes, and soups have sodium to help retain the water.
Your stomach may be feeling queasy and eating may be one of the last things on your mind, but it certainly helps. Everyone has their own "hangover" food so go with whatever works for you. Try to focus on getting lots of protein and carbs. Also, it is interesting to note there have been studies that show that not only eating bacon but also the smell of bacon cooking helps to alleviate a hangover.
If your head is pounding, you'll want to take a pain reliever. Ibuprofen (Advil or Motrin) or Aspirin is fine, but stay away from Acetaminophen (Tylenol or Excedrin)--your liver cannot process liquor and acetaminophen at the same time, so combining the two will wreck havoc on your liver!
Hangovers are also caused by vitamin depletion. If your stomach can handle it try taking a multivitamin. You should also take Vitamin C and Vitamin B complex, as the deficiency in Vitamin C and especially Vitamin B causes hangover symptoms. Primrose Oil supplements as well as Milk Thistle have been found to help cure hangovers.
If you have the energy to make one or can get someone else to make one for you, a smoothie is a great way to easily get all of the nutrients you need to replenish your system into your body without too much effort. Ingredients to include in your smoothie that either help cure a hangover or will help protect your liver include: bananas, strawberries, honey, almonds, milk, and orange juice.
Lycopene is a carotene that not only helps prevent aging, but helps cure hangovers. It is most commonly found in tomatoes and has the best effect in slightly cooked tomatoes. This is why a bloody mary so commonly helps with hangovers, it isn't the "hair of the dog" but rather the lycopene in the tomato juice. Lycopene is not only found in tomatoes but also in other red fruits & vegetables, such as red carrots, watermelons and papayas (but not strawberries or cherries).
Hangovers are also caused by a mineral deficiency which can be rectified by eating pickles or other pickled foods. Pickles are especially easy and good to eat while hungover because they are cold, light, salty, and have a high water content.
I have never had the energy or ability to exercise while hungover, however many people swear by it as it helps you sweat the toxins out.
Getting in the shower and switching between hot and cold helps alleviate a hangover as well.