Dr Gray was absolutely amazing. I had been skiing for 30 years and never had high altitude sickness. Had no idea what was happening...wasn't too far from passing out as my blood 02 was so low. My friend thought she had called an ambulance...and mistakenly had called Dr. Gray. Literally...within 20-30 minutes, I was fine. We kept the O2 machine our entire trip and never felt better skiing in my life. We will use him everytime we go from now on...such a neat guy, too.