If you're traveling to mountainous areas this summer, get used to the new heights before starting any strenuous activities, advises the University of Maryland. By not allowing your body time to adapt to a new altitude, you risk developing acute mountain sickness, which can result in headache, nausea, vomiting, insomnia, fatigue, and increased respiration and heart rate. These symptoms will generally resolve themselves if you rest, drink lots of fluids, and eat a high-carbohydrate diet. Severe altitude sickness can lead to fluid in your lungs or swelling in your brain. The best treatment is to get to a lower altitude as quickly as possible.