I can attest that AMS can sneak up on you if you don't respect it. It has happened to me a few times, with symptoms of fatigue, periods of dizziness and headache. Each time I got the clue and headed for lower altitude. It's so unpredictable. Most ski days I can head up to the mountain and take the chairs up to ~9000ft 1st thing. But every once in a blue moon my body can't tolerate the change - even though I'm feeling great getting on the lift for the ride up.
Also, when folks come to visit during the ski season, they'll sometimes stay at a condo/lodge nearer the resort - which is at 4000-5000ft. It's pretty common for one or more of the folks to go through the fatigue phase the first couple days or so, which puts a bit of a damper on things for them.
So, this does touch on a little discussed reality for ski vacation planning: it's wise to include some degree of elevation acclimatization time in the schedule and your skiing strategy.
Elevation acclimation is hard to do if you are in Colorado for 5 days and the place you are staying is already at 9100 ft. We were on vacation in Summit County and drove straight to Dillon which is at 9100 ft. In Denver, we were fine, however in Dillon bringing suit cases up two flights of steps was exhausting. While we slept, we also found ourselves gasping for air. As a result, we researched altitude issues and water water water is key. We ate bananas before skiing for energy and potassium. We also took Altitude Adapt (nitric oxide) which we found to be helpful. However, when we skied A Basin we bought oxygen and would go in and take a few breaths from the can. It took me about 2-3 days to adapt to Dillon's elevation.
Do not be fooled by acclimating in Denver. Altitude is not really felt there a whole lot unless doing something strenuous. It may cause people to think that they feel fine there but remember Denver is around 5280 ft but it is not until after the
human body reaches around 2,100 m (7,000 feet) above sea level that the saturation of oxyhemoglobin begins to plummet. After we vacationed here, we moved to Colorado and now live at nearly 7000 ft and have found that it does not bother us too much, however, when we ski and are starting at elevations above 9000 ft and often above 10000 ft, we still get short winded. To this day, we continue to drink water and eat bananas before we ski.
When ever anyone comes to visit, we have then take Ginkgo Biloba and Ginseng daily for a week or two before arriving. We did this before moving here and from to visitors who took it vs those who did not, the results have been great.
Blog post about Altitude Adapt
http://briangreen.net/2013/08/altitude-adapt-reader-testimonial.html
Summit County Elevations
Arapaho Basin Base Elevation - 10,780 Feet
Breckenridge Base Elevation - 9,603 Feet
Copper Mountain Base Elevation - 9,712 Feet
Keystone Base Elevation - 9,280 Feet
Loveland Ski Area Base Elevation - 10,800 Feet
Dillon Elevation - 9,111 Feet
Frisco Elevation - 9,075 Feet
Silverthorne Elevation - 8,730 Feet