Yeah – altitude sickness is terrible for those afflicted! I pretty tolerant, but I learned in college that many are not We didn’t do anything illegal or really dangerous, just dumb.
My hiking buddy and I spent a week in RMNP. Toward the end of the trip, we took a circuitous, three day route on our way to climb Longs Peak (14,259 ft). We had book-packs, childhood sleepover sleeping bags, and a cheap dome tent. We didn’t bring nearly enough water, so we drank from the streams along the way. Neither of us got giardiasis, fortunately.
We camped the night in the boulder field at the base of Long’s at 12,400 feet. We survived a really long, cold night, but my friend awoke to a headache and nausea. He convinced me to go on up alone while he waited in the campsite. I returned a few hours later to find a lot of undigested breakfast scattered around, but no friend. I ended up trying to catch him on the hike down, but the only evidence I saw proving he was still alive was intermittent splashes of vomit. I finally caught up to him at the parking lot.
He couldn’t tolerate any food, and could barely even keep water down, though we had descended to 8500 ft. We “slept” that night in the car, with him throwing up every hour or so. His nausea didn’t subside until well into the drive home as we neared sea level. His experience made me very aware of the need to acclimate and hydrate whenever I go up that high. Everest, anyone?