Starfish,
I am not in any way dismissing your fears or anxiety. I know this is going to be a tough ride, but remember you have trained hard and just do the best you can. Try and relax.
That said...
You actually can not feel any effects of altitude under 5280 feet. That is only if you are highly sensitive. The average person does not begin to feel them until about 8000 feet. The only exception is in the polar regions where you can feel effects as low as 4000 feet.
That of course is not to say that you are not having any physical symptoms. It is amazing what stress can do to our bodies. I just hope it makes you feel better to know that it doesn't have anything to do with the altitude.
Best of Luck to you.