The simple answer, from experience, is that you are experiencing a cerebral allergy. From here it gets slightly more complicated. It has been said that often what we crave is what we are allergic/intolerant to. One thing to note, is that often what we are allergic/intolerant to, is what we are in need of. This was a personal experience with fats. For years they made me worse. Once I started getting better, fats started giving me huge improvements. My face would droop similarly, with a rhinitic effect as well, not to mention the brain fog.
So, the tricky part is how to overcome the paradox. At first, I would recommend avoiding anything that aggravates you. At one point, I had gone from a almost 200lbs of muscle at 5'6, to 110-115lb, and reacted to every thing but rice cakes, Sea Salt and water(which became a diet for 3.5months). The purpose of that, is to aid in decreasing strain on both the adrenals and immune system(along with liver and gut). As your natural anti-inflammatory processes slowly restore, reactions will diminish. Your gut will heal, and cellular energy will become available for digestion and repair.
Along with a non-reactive diet, killing the microbes in a calculated manner is essential. By calculated, I mean, at a pace that die-off reactions are not dumping excessive toxins back into your body faster than your potentially compromised liver and gut can handle their breakdown. Also, monitor drooping in your face, etc during this time and see if there is any cross-correlation.
Once this is done(or simultaneously), take anti-oxidants for the oxidative stress, boost cellular energy to improve mitochondrial function, cleanse liver in non-aggressive manner, reinnoculate with good bacteria, while healing both the lining of the gut and the adrenals.
Hopefully at this point, small amounts of fat will be tolerated, thus healing anything with a lipid-layer(basically, every cell). This will also now aid in the inflammatory process it once caused, and things can come full circle. As a side note, the brain is over 50% fats, so if there is a hyper-reactive region of the brain that has been turned on by physical, chemical, or emotional stress, this can also feed the malfunctioning region/organ. That being said, trying dhea or inhibitory neurotransmitters to calm an over-excited brain heals some of MCS, etc.
This is extremely frustrating, but is temporary. I hope this helps, and if not, I'm sure you will find the pieces to your puzzle. This is a great site full of great info.