Today's breathable air contains less than 21% oxygen while previous years contained more than 50%. Big city living or being at high altitude decrease your oxygen intake even more. Your body thrives on three things; 1) oxygen, 2) water and 3) food. However, oxygen is the catalyst for the other two. Without the proper levels of oxygen, your cells become less efficient and slowly turn into sick cells. If you were able to consume more oxygen per breath and develop a better breathing technique, your cells will reproduce and grow making your body and mind stronger and healthier.
Approximately 40% of us that travel to resorts with elevations of 6,000 feet or get symptoms of altitude sickness or AMS (Acute Mountain Sickness). Within the first 3 days, you can experience headaches, fatigue, shortness of breath, nausea, poor appetite and insomnia. Many who go on trips to the mountains experience some of these symptoms without knowing what causes them. Altitude sickness can look and feel like the "flu". In more severe cases, thinking and judgment may become impaired and about 1% of these people will develop more serious conditions and can become fatal.
Once symptoms occur, they may improve over several days. However, if symptoms do not improve, they may be relieved with the administration of oxygen or descent to a lower altitude. When in doubt, see a physician.