Well,
What an interesting sub-topic this has turned out to be!
I have had a quick read through the on-line literature on altitude sickness this morning. There is quite a lot of it. I think the most helpful phrase was 'the causes of altitude sickness are not fully understood'!
It seems to be partly due to the dryness of the air, increasing the likelihood of dehydration and nose-bleeds, and partly due to the drop in air pressure resulting in a drop in the actual number of oxygen molecules available to us in each breath (although apparently the percentage of oxygen in the air remains the same up to 70,000 feet).
I have observed the drop in air pressure by its effect on things like my roll-on deodorant (the ball fell out), pre-packed food in the shop where the plastic bag hugely over inflates etc.
Less oxygen available makes the heart work harder, increasing one's pulse and respiratory rate. I have noticed this myself. Running up the stairs in the apartment in the resort makes me quite out of breath. And presumably it is the reduction in oxygen that causes the mental confusion.
What I didn't know, though, is that altitude can cause swelling of the face, hands and feet and a weight gain of 4-12 Lbs. I also didn't know that it can affect the medication you take - for example, warfarin and other blood thinners may be more active at high altitude.
There are a number of other effects listed as well, like insomnia (I tend to wake up in the middle of the night), drowsiness (another problem I have in the evening), and then rather frightening more severe reactions (which I hope only occur at very high altitudes) like fever, vomiting and even death :shock:
I think myself the nosebleeds are caused by a combination of the dry air and your heart working harder. Apparently there is a high concentration of blood vessels just beneath the lining of the nose, which can bleed relatively easily.
The general advice to reduce the symptoms of altitude sickness is
a) Acclimatize yourself gradually to the altitude (not really practical on a ski holiday, apart from ski-ing the lower runs first)
b) Cut down on your alcohol intake.
c) Drink plenty of water throughout the day - at least 6-8 glasses
d) Use a humidifier in your room, or find another way of increasing the relative humidity of your room (like drying things on the radiator I suppose, or boiling saucepans).
http://www.answers.com/topic/altitude-sickness
Ally