I'm considered "mild case", but had been in the Colorado Springs area for about a week-long period, and had only encountered trouble when I did a 200 meter dash, one time!
One of the major things about the high elevation is the necessity to take on lots of water, to avoid dehydration.
During one of my several visits in Colorado Springs, I've seen a lot of elderly walking around with oxygen tanks, including my parents.
The one time I brought my new wife, we found out she was sensitive to the high altitude and had to "suck" on some O2 for a while, and I even took a few "tokes" before bed at night, for safe measures (and because the O2 was available).
There is one member on here from the Denver area (Denver is slightly lower in altitude than Colorado Springs), he goes by the name of "Mockingbird". He might be worth asking, if he doesn't happen to come across this post, first.
I hope this is a start for helpful information.