Hi. I went up a flight of stairs in Tahoe last week at an elevation of 6200 . When I got to the top of the stairs, my heart began fluttering, and I had a sudden pulsating mildly painful throbbing in the lower back. It stopped after a couple of minutes of rest. But, the episodes de concerns me. I m 62, with diagnosed COPD, 5 8 175 lbs.