If in spite of all these precautions you were to suffer a stomach problem (a rather usual malady amongst travellers), drink plenty of purified water and anti-acids after each meal. If the problem persists ask a doctor.
How do I avoid sunburn?
Take into consideration that the ideal way to get a nice suntan is by exposing oneself to the sunrays during short time periods first, to then start prolonging them progressively to prevent the skin from being damaged by the sun. Therefore, try not to be overexposed under the rays of king sun for the first days. Do not fail to use sunscreen and to drink abundant water to keep your skin hydrated. Do not hesitate to ask for medical assistance if you were to suffer sunburns or erythemas. Remember that big hotels have health professionals working 24 hours a day.
What should I do if I am smarted by a jellyfish?
If you were to be smarted by an aguamala (a type of jellyfish), get out of the water until the itch diminishes. It is advisable to apply humid sand or abundant apple vinegar on the injured area. In case these homemade remedies did not work, go and see a doctor.