This condition, also known as mountain sickness, occurs in mountain climbers or hikers who have climbed too quickly to heights above 3,000 metres, thus failing to allow their bodies to acclimatise to altitude. The lower atmospheric pressure and shortage of oxygen result in hyperventilation – deep, quick breathing – and this reduces the amount of carbon dioxide in the blood. Nausea, anxiety and exhaustion are presenting symptoms, as is confusion and unsteadiness due to cerebral oedema (See BRAIN, DISEASES OF) and seriously affected individuals may be acutely breathless because of pulmonary oedema (excess fluid in the lungs). Gradual climbing over two or three days should prevent mountain sickness. In serious cases the individual must be brought down to hospital urgently. Most attacks, however, are mild. Treatment is by inhalation of oxygen, gradual descent and taking a diuretic such as ACETAZOLAMIDE.