Get educated about altitude. As altitude increases, air pressure decreases, resulting in less oxygen available with each breath. The relative lack of oxygen can cause altitude sickness, especially at altitudes above 8,000 feet. Symptoms of mild altitude sickness include, nausea, headache, lack of appetite, fatigue and dizziness. More severe forms of altitude sickness are High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema (HACE), which can be fatal. Everyone attempting to climb a fourteener should go with a group, and everyone in the group should know the symptoms of severe altitude sickness. Sometimes the mental confusion associated with altitude sickness causes victims to isolate themselves from others, so it is important for people in the group to keep their eyes on each other.