Absence of oxygen could cause faint or apnea without any sings and symptoms. But actually people will obtain the oxygen through breath taking and hate rate increasing.
So the main reason of High Altitude Sickness (Acute Mountain Sickness) is decreasing of carbon dioxide concentration.
There is no direct relation among ages, sex and personal physical ability with high altitude sickness. Athletes and youth will suffer the Acute Mountain Sickness if they don't prepare well or ascend too fast.
In fact, High Altitude Pulmonary Edema and High Altitude Cerebral Edema are two life-threatening sicknesses to people. But high plateau is not life-threatening to everyone.
The signs and symptoms of high altitude sickness are common to people and it is usually covered after you back to lower altitude. The severe Acute Mountain Sickness often happened to people who insist on ascending higher even though they already suffer the symptoms, or people who can not back to lower places immediately.
If you have healthy bodies without any severe diseases, Tibet, Nepal, Peru, Bolivia are the worthy to go.
Sherpas of Nepalese really fits the high altitude about 4000-5000m, but most of Nepalese do not have the talent to high altitude.
The signs and symptoms of Acute Mountain Sickness usually occur after few hours or days. The most dangerous time is the first night arrival in high altitude. Even you have been to high plateau of 5000m, you may suffer the high altitude sickness in plateau of 4000m next time.
People will be gasped without absence of oxygen but you will feel better after a rest. Therefore people are kindly suggested to take many sports in your daily life to improve your pulmonary ability.
If you only suffer the pant, it is not the decisive evidence of Acute Mountain Sickness.