Why do people get altitude sickness?

Lack of Oxygen. The higher the altitude the less Oxygen there is. Therefore our body has difficulty adjusting to the amount of Oxygen that receives. Our brain gets the signal first and foremost and create symptoms like light headiness, dizzy spells, nausea, fainting...

The percentage of oxygen in the atmosphere at sea level is about 21% and the barometric pressure is around 760 mmHg. Although the percentage remains the same as altitude increases, the number of oxygen molecules per breath is reduced. For instance, at 12,000ft the barometric pressure is only about 480 mmHg - that means roughly 40% fewer oxygen molecules per breath, so the body must adjust to having less oxygen. The sickness is usually caused by going too high too quickly; if we give ourselves time to become acclimatised at a particular altitude (generally 1 - 3 days), before moving higher, our body will adapt to the change and sickness will be avoided.

There is a lack of oxygen at altitude so if your brain doesn't get enough oxygen you get ill and I believe you can get blood clots also. People who are born at altitude are OK.

when there is not enough oxygen, our body starts fermentation and makes some stuff instead of energy for cells so we fill dizzy and tired. we should ascend gradualy so the body gets use to lake of oxygen.

lol When I first read this I thought it said attitude sickness :D Um.. because the air is thinner, so it makes you have a loss of air, which makes you feel sickly

lack of oxygen. You get dizzy

I guess it has something with natural fears of danger , because we are meant to walk the earth not to fly.. well that's what I think.

dunno.....i do