Montezuma's Revenge is not:
* A vengeful ghost intent on human sacrifice;
* Some kind of vague, non-specific scam enacted by all Mexicans against all tourists;
* A curse which brings bad luck to anyone visiting a certain site or touching a certain rock.
All of the above are your internet friends trying to troll you. The real Montezuma's Revenge is a lot murkier than that. It's traveler's diarrhea.
Wherever we live, our bodies become used to the local water and the local food. People generally think that water is largely tasteless, until they travel to another city or state, even within their own country. That's when the discovery is made that water can be 'hard' or 'soft', or have discernibly different aftertastes, depending upon which filtering and cleaning chemicals are used by which local authority. 'Hard' water will have a higher mineral content than 'soft' water. But if the water is too soft, it might erode our household plumbing. Some processing plants are required, by local law, to add extra chemicals, if there's a profusion of fungi or algae caused by your landscape.
However the water is treated, we each build an immunity to all that's in it. Our bodies recognize that this is how water should taste and those are the minerals and chemicals that should be in it. They cause us no harm (no water processing plant is going to add harmful chemicals!) and life goes on. Until, that is, we go on vacation. Suddenly we have a whole different kind of water and our bodies have to suddenly reassess the situation. For some, with robust constitutions, this change happens with no side-effects at all; but for those with more fragile stomachs, their bodies can panic. They will treat the difference as poison and try to expel it from themselves. Hence the diarrhea.
This isn't a problem peculiar to Mexico. It simply seems that way, because this is the vacation destination for millions of Americans, Canadians and those further afield around the world. This might be the only time that those tourists drink water that is treated differently to that at home. However, it's not called Montezuma's Revenge everywhere. The Turkish Two-Step; Bali Belly; Pharaoh's Revenge/Cairo Two-Step; Kurtz Hurtz (Uzbekistan); Beaver Fever (Canada); Katmandu Quickstep, are just a selection of the alternative names for traveller's diarrhea. It happens wherever people drink different water or eat different food to that which their body has formed its immunity.
It is referred to as Montezuma's Revenge, when it occurs in Mexico, because of the Aztec Emperor, Montezuma II. He is alternatively known as Moctezuma II and his story was told in a previous blog entry: Mexico City - The City of the Gods. The short version is that he was the Aztec ruler at the coming of the Spanish. It was his empire that was over-run by the invasion force of Hernán Cortés. Montezuma II fought back valiantly against the conquistadors, but the upshot was that he lived to see his empire in foreign hands and he died in chains under their rule.
If the spirit of Montezuma II was wishing to wreak revenge upon the modern invaders (tourists), then it could be imagined that it would be more bloody than an upset stomach. Nevertheless, the wry moniker 'Montezuma's Revenge' has been applied to just that.
No resort, nor business reliant on the tourist trade, wants to see their clientele confined to their bathrooms, groaning. Therefore, you will find plentiful bottled water in Mexico, particularly where those on vacation congregate. Drink only this, rather than water from the faucet/tap and you'll be fine.
Ensure that you also brush your teeth in bottled water, plus that the ice in your drinks is from bottled water, for that extra security. If you are self-catering, then only wash your food in bottled water. You get the general idea! The restaurants and other eateries, in the tourist zones, will be using this in their food preparation anyway, as they are the last people who want to be accused of causing Montezuma's Revenge. Therefore areas like Cancún see very few cases of traveller's diarrhea.
If you do end up as one of the 20% of vacationers, travelling world-wide, to fall foul of traveller's diarrhea, then don't panic. It is inconvenient and downright disappointing, when you've saved up to come away, but it's usually easily treated.
Symptoms are loose bowels; abdominal cramps; nausea; and a bloating feeling. All of the above are your body's way of trying to expel something, which it considers poisonous, from your system. It is not contagious, so milk it for all the sympathy that you can get from the rest of your party; but equally don't be afraid to allow them back out into the wide world. They will not be carrying some dire virus. By the same token, if you can find somewhere with easy access to a bathroom, then you can go out yourself.
The most important treatment is fluids. Drink as much bottled water as is comfortable, so to flush out your system, and replace all of those fluids that you are losing by other means. You are also losing salts, so water primed with hydration salts is the best of all. Try to avoid alcohol, as a main way to take on fluids, as that can actually dehydrate you. Bottled soda works for some, but not others.
It might be worth a visit to the local drug store/pharmacy/chemist, as they would be well aware of the local variation of traveller's diarrhea. You might be able to get something over the counter to hurry along your body's stablization. It may take anywhere between one and five days to feel right again; with the average being 3.6 days.
If the symptoms are very severe, or there is blood in your stools or a high fever, then seek urgent medical advice. It might not be traveller's diarrhea, but indicative of something else.
Here's hoping that you never get traveller's diarrhea in Mexico. But if you do, at least you now know that it's only the occasional uncomfortable rush to the bathroom, and not the dismembering wrath of an Aztec king.