Well, when muscles don't work, they don't "pump" the circulation as well (technically the heart is the pump of the body). And standing up drains blood downward. You may not be getting enough circulating due to it "pooling" in your limbs. And if you are dehydrated, it will be so bad that you may feel faint.

The only thing I can liken it to is when I was dehydrated from undiagnosed diabetes insipidus (water diabetes where you don't have enough diurectic hormone to absorb water). I felt like the life was sucked out of me all the time. And it wasn't only water but electrolytes that were off.

I'm with Tyson, I don't know how you can stand on your feet that long! I can't do it for long at all.

And when you stand, you use a lot more muscle strength and your MG will get worse.

I hope you will talk to your doctor about it.

Annie