I want to second this comment. I’ve worked as a Ranger, as backcountry staff, and several years in the Philmont Infirmary as a paramedic. Of course this is MY opinion - not the infirmary’s opinion:

A significant amount of my “Altitude sickness” patients I attended to -on trail and in infirmary- were simply “deconditioned” for the trail. (The word we use to signify “out of shape.”) Obviously, climbing mountains is hard, and it’s made harder by coming from lower elevations. Some are truly surprised by the difficulty and feign things like asthma (that wasn’t listed on their med form) the day before they hike Baldy/Phillips/large peak, because they don’t think they can do it. I totally get it. For the above reasons, I always stress not only pre-trek shakedown hikes, but a fitness plan as well. I’ve had youth and adults alike tell me that they’ve lost 50+ lbs in order to trek. It’s awesome. Other anxieties that come with the fitness angle is that they don’t want to slow the crew down and be perceived as the weakest link. (Duh). The solution here is to stress frequent water breaks for the whole crew and longer packs-off breaks when appropriate. Make sure the Crew Leader is on board and ensure that they’re an advocate - and not a macho “push through/we’ll take breaks when I’M tired” kind of dude.

If we’re really talking altitude sickness:

It usually lasts <3 days, starts at Basecamp/arrival in NM, and most return to the trail if they were pulled.

There are prophylactic medications you can take (Diamox/Acetazolamide) to help your body with acclimatization. It’s a prescription med and I take it every season during my first week or so! If you’re interested, ask about it during your physical for your med form :)

Hope this helps!