When you drive above 5,000 feet, there is substantially less oxygen available and you can become very quickly?

you can become TIRED very quickly. As one ascends towards the sky, the quantity of oxygen available continues to reduce significantly and this have a lot of negative effects on humans. For instance, there will be less oxygen available for breathing and one can become tired quickly. The lack of oxygen can cause shortness of breath, nosebleed, headaches and increased heart rate. Also, the air becomes drier and this makes one to become unusually thirst.