As has been said, drink plenty of water!! Also, time is needed to aclimate to the elevation. I live at 6000 feet and work at 6500. I camped this year for my elk hunt at just over 8000, and we hunted at about 10,000 feet. It still took my a couple of days to fully adjust, but I was drinking plenty of water. I also have a reduced lung capacity due to a month and a half long bout I had with pneumonia in 2003. There is a bunch of scar tissue that will neverrepair itself, nor be replaced, so I have to live withit.

I would recommend the next time you head out west, to go at least 2 days early to adjust. If your body doesn't adjust, it can not only be a pain, but be FATAL!! Good luck