The symptoms include staggering, confusion, and hallucinations. The only cure is to move to lower altitudes right away. If you can't get down fast enough it may help to go on bottled oxygen or spend some time in a Gamow bag, a portable pressurization chamber that artificially increases the atmospheric pressure, simulating a lower altitude. In extreme cases you could also inject dexamethasone. Dex is a steroid that can temporarily negate the effects of altitude, giving a climber time to make it down the mountain.
Climbers often carry a vial of dex under their down suits as a precaution.
All About Altitude Illness Altitude Illness from emedicine online Altitude Illness Advice High Altitude Mountaineering Safety Outdoor Action Guide to High Altitude One of the odd things about altitude sickness is that it's unpredictable. Even Sherpas, whose bodies are well adapted to these heights after generations of living at altitude, can be struck with these illnesses. But all climbers take precautions to lessen the perils. They spend time at various levels to let their bodies adjust to the thinner air. They will stay at Basecamp, where there is half the amount of oxygen available at sea level, for several days before heading up to Camp I for an overnight stay.