Hi there :)
Ive the same with this illness. Standing more than a few minutes is so bad .. much harder than walking. I struggle whenever I need to wait in any queues etc.
I not only get dizzy but standing for any length of time makes me feel like im going to go into a seizure. I actually do start to tremor and shake when that feeling comes in, I have collapsed.
(I often end up having to sit on the ground, grab a chair if there is any about the place eg in government depts., end up holding onto something or just leave the queue... I just cant stand there).
Its hard.. as others dont understand how hard it is for me to wait for service in shops.
For an explaination of what the trouble may be..do a search for " Dr Cheney "(he's a famous CFS researcher) and the articles " the heart of the Matter: CFS and Cardiac Issues " It will probably make heaps of sense to you and give you a better understanding.
(I would post a link but I dont know if its against rules or not..so wont).