I had a period of time that was called orthostatic hypotension, where my blood pressure would tank and I would pass out on flights over 3 hours. I would suddenly get a feeling of being cold and hot at the same time and feeling like I was going to toss my cookies. I learned on a Virgin Atlantic Flight not to get up as I awoke on the floor with some concerned flight attendants staring at me. Another time I threw up while I was passed out and lost all other bodily fluids as well on a United Flight from Chicago to LAX on the way to OZ. They basically tossed me off the plane and into the terminal, where I sent Mom to buy new clothes in the gift shop.
After several doctors told me I must be afraid to fly and gave me xanax (I have skydived before so I am not afraid) I read somewhere a list of things to do and it has worked since. I don't do any caffeine, artificial sweeteners or alcohol for 48 hours preflight. I wear compression stockings to keep the blood out of my legs and also on occasion have taken salt tablets before boarding. It works for me.

JudyJFLA