Okay, take this with *many* grains of salt.
I have experienced symptoms very much like what you have. I went to several doctors and never had it adequately diagnosed. I have found two things that seem to help. You might feel they are unnecessary, irrelevant and/or quackery but I believe they helped me.
First, I want to ask you if while you were in the intense pain were you not able to get anything down? Even water? That's how it was for me. I couldn't take anti-acids or anything at all. This made it impossible to take the usual remedies, and when I could get them down they didn't help.
After all the various (wrong) diagnoses by MD's, I finally I went to an alternative medicine practitioner and what he had me do worked for me. For the actual symptoms while it was happening I took a specific homeopathic remedy. It was the tissue salt Kali-Sulph. They are very small tablets of mostly sugar that you take, 4 at a time, and hold under your tongue to dissolve. You don't swallow them. I would take 4 and wait just a few minutes and the symptoms would be reduced for a while. When they came back I took 4 more. The idea is to wait longer and longer between doses. For example if you have to take the second dose 10 minutes after the first, see if you can wait 20 minutes to take the next, and so on.
The other thing I did was to stop eating meat of any kind (yes that means seafood too). This stopped the attacks completely and after about a year I began eating seafood again and years later eventually began eating all kinds of meat again.
I have never had an attack as bad as the ones I used to get but I keep the Kali-Sulph around just in case and it has been very handy on a few occasions where it felt like I was headed for another attack.
Just to repeat the disclaimer, I believe this worked for me. I would hate to have you do this and not get it looked at by a doctor. I did this after being told it was a variety of things by doctors that just wouldn't admit that they couldn't find anything. In your case, there may be something very serious that they will find.
Good luck!