I'm 18 years old and I've always been in pretty good physical shape. I have also had a somewhat noticible increase in my heart rate when getting up from a lying down position, and a slight intolerance to too much physical exercise, throughout much of my life. Recently however, the tachycardia has gotten much worse.
I have to get up extremely slowly and usually have to hold on to something as my heart starts pounding and my vision greys-out to the point I can't see. (I'm guessing the vision's from hypoxia). My breathing becomes very rapid and I get extremely tired.
The severity isn't always the same, but it's getting hard for me to do anything physical, even standing. I can barely make it up a flight of stairs and I'm tired all the time.
My blood pressure is normal & it does not change when I change positions. However, my pulse rate increases by 20-40bpm with a change from sitting to standing.
Does anyone have any ideas on what this could be?