Your symptoms sound like my Dysautonomia. I have POTS which is a type of Dysautonomia. You stand and the pulse is 30 or more beats more than sitting or lying down.

You feel lightheaded standing? Have you taken your bp and heart rate sitting and standing? I was bedridden, then in a wheelchair with this. Now I can walk a lot, but in large places, I use a scooter or w.chair. My heart rate climbs if I try to do things like clean or use my arms a lot. Hubby does a lot, but we have house cleaners do the cleaning since he works all day.

You can look at Dinet.org to see if the information helps you.