Hey Nmac, hope you are as well as you can be today, I have a Mitochondrial Myopathy and M.A.D.D., and know that any of my muscles whether skeletal or organs can be affected, my problem is my heart rate being high, even with meds, and just sitting I am at 100 BPM which is okay as it used to go up to between 140 and 150, so I get E.C.H.O.'s every one or two years to keep an eye on that heart muscle as it can't be a good thing for it to be so high all the time. But I too worry as to O2 and I hope you get to the bottom of this as it must be awful to deal with (and tiring which is already a challenge for Mito patients, but if your blood isn't being oxygenated enough I expect that can lead the body to become very sluggish, I may be wrong, but it sounds very tiring). So I hope you find out soon what is causing this problem and you can get the help you need for this, my O2 levels do get lower when I am ill but not to the depth you and others are dealing with, sending you hope.