Flights to cities at relatively high altitudes, such as Quito, Ecuador and Cusco, Peru, bring one from sea level to thousands of feet above in a matter of hours. Without sufficient time to acclimatize, the body can react with headaches, general sickness, difficulty breathing and worse. Plan your itinerary to ascend as gradually as possible and on arrival, move with minimal exertion and hydrate. Consult your physician before travel and consider bringing medication.