I worked a job in New Guinea when I was in my thirties. The elevation was at 12000'. I had sever symptoms of altitude sickness at night and would wake up gasping for air. It makes it hard to get a nights rest. I finally relocated to accommodations at 8000'. That was a cake walk compared to 12000'. Now 40 years later I cannot handle 8000' elevations even walking. I have to stop and get my breathe frequently. Seven thousand feet elevation works much better for me. I do use O2 for sleeping tho. You may have to consider O2 when you are at higher elevations. I do fine below 5-6000'. Good luck.