The most common health issues involve sanitation and associated intestinal ailments. In addition, most travelers want to know about vaccinations and prophylactics against tropical diseases. At higher elevations less oxygen is available for the body's use. This can lead to swelling of the brain tissue which causes severe headache, nausea and vomiting. More severe cases can lead to the leakage of liquid into the lungs.
Prevention is the key.
When arriving at high altitude let your body get used to it. Take it easy, avoid alcohol and smoking. If symptoms develop, Diamox can help mild cases. For more severe cases, descend to lower altitudes ASAP and seek medical attention. None are generally required though some recommend vaccinations against yellow fever and typhoid.