Several people are taken by the increase in their local altitude when the arrive in the 7,000 to 10,000 ft. main street of the ski towns of the rockies. Jet lag can add to the symptoms experienced from the less dense air. Caffeine, Nicotine, and Alcohol all impede adjustment to the new altitude. Alcohol especially, when you first arrive a mile or two above sea level one drink carries the punch of two. Obviously your ski equipment is very important.
Boots are the most important piece of equipment.
Always try on both boots, walk around in them, etc. Start with the boot loose, then tighten over several minuets. One of the to keys boot fit is a lack of heal lift. Most ski shops realize that this is a service industry but some just want to crank out numbers. If your buying boots, again fit is primary.