We live in Colorado so I’m very familiar w/altitude sickness -especially when our friends & family come to visit from the east coast.  I would definitely think it’s altitude sickness that bothered him.  I don’t know about those with CAH being more affected by it, but I would definitely see where they would get more dehydrated quickly & you would want to take extra precautions such as having a gatorade type drink with, having the solu-cortef just incase....Just a non CAH-side note, when we first moved here & started heading up into the mountains for trips, I experienced similar symptoms (I do not have CAH) & got migraines almost each time that first year.  We’ll see how it all works out for our SWCAH son -he is only 20 months old.  Maybe being born here, he won’t have a problem.  Best wishes!  What a scary situation.  Glad he’s feeling better!