I am 82. I work out, I stretch (ballet stretches), I lift 10 lbs. on each wrist and do supported jumps with 5 lbs on each ankle. I walk, I bike against the wind. Lately I am experiencing rapid heart rate (115 with pulse oximeter) when I am doing very little. Rising and walking into the kitchen can do it. But it is more than orthostatic hypotension because it happens when I am already moving. All my tests are always normal. A nurse told me she wanted to be me when she grew up. What could be the problem? I am 4 ft. 11 inch., weigh 113.