I live pretty close to sea level, so hiking at that elevation probably would have killed me. :P Sounds like quite a jaunt, though. I haven't been on a night hike in forever.
I used to live at sea level, and when I did, 8000ft+ would really knock me out. Now that I live around 6500ft, my tolerance went up a little, but hiking over 10000ft still knocks me out. But ~6000ft never bothered me, even when I was living at sea level.
At least there weren't nettles.