I would pull out all the stops, as I am sure you are doing. You have anxiety and control issues -- you're really embarrassed even to be telling them this information -- and any change of any sort that's out of your control makes you physically sick. You haven't been sleeping. You worry that you will "freak out" on the plane and ruin the flight for all your fellow passengers if you have to go on this flight that has been changed outside your locus of control. .... I suppose that this approach could fail or even backfire,
But if you're trying everything, why not this.
I would be happy to hear others' strategies, too.