I know you were tested for allergies but.. almost sounds like a really bad food intolerance or food allergy you haven't found yet.. :S
I react terribly to maltodextrin.. and oats.. it's stupid but I went on a food allergy diet (you can google it..)
I've heard from others that if you ate nothing but pears and turkey those are the two most allergic free foods you can do.. for severe cases I wonder if you could handle that diet for like 3 days and then introduce... meat.. chicken... and just build from there and see if your IBS/anxiety and panic attacks go away...?
Just a thought but your reactions to me sound like allergy to foods..maybe a cousin food... beans or something that you're still eating (hopefully it's not like a corn allergy.. I've heard people having that and that's like the toughest one to avoid!) :S
Good luck :(
google neurocardiogenic syncope
Do you drink coffee or cola drinks? Have you ever stopped them? I know it sounds silly, but just stopping coffee and starting Metamucil 5 capsules before bed with water solved his problems. He was shocked that it was the coffee. The Metamucil forms a gel in your stomach, so I guess it keeps splashing from happening at night. It also helps with high cholesterol and keeps things moving for most people. It also helps with diarrhea, oddly enough.
If it helps, but not completely, perhaps there is something else like citrus that you eat all the time that you could eliminate. My boyfriend is allergic to all fruit, and hives is a symptom of some of them.
Please give this a try for a week and see if you don't feel better.