Altitude SicknessAltitude sickness, also known as mountain sickness, is caused by insufficient oxygen at high elevations. It causes such symptoms as dizziness, shortness of breath, and confusion, and can strike campers at relatively low elevations of about 2400 m (about 8000 ft). Campers who plan to backpack at higher altitudes often take a day or two to become accustomed to their new environment. They hike slowly when going higher—typically gaining no more than 300 m (1000 feet) in elevation a day. If they develop symptoms of altitude sickness, they should descend to a lower altitude quickly, before the condition becomes life-threatening.