Acute Abdominal Pain: Every so often, out of nowhere, usually in the middle of the night, I wake up with the ?

Every so often, out of nowhere, usually in the middle of the night, I wake up with the most severe abdominal pain I have ever felt in my life! It comes on very suddenly and feels like labor pain. (No, I am not pregnant) There is very little warning. Within 10 minutes I am keeled over in pain in the upper abdomen. I have had many, many tests. So, I will tell you what it's not...it's not an ectopic pregnancy, or gall bladder, appendix, or any other organ problem. It's not diverticulitis or Crohn's or Acid Reflux. It's not IBS or anything I ate or drank. Aside from the severe pain, there's also nausea, cramping, constipation that eventually subsides to diarrhea. I also break out into a cold sweat, soaking wet, and I get the shakes. I can actually feel the spasms working it's way through my gut. I have had blood tests, CT Scans, Sonograms, Swallowed the Camera, Colonoscopy, and Endoscopy. All showed normal findings. I was just prescribed an antispasmatic drug that I put under my tongue at onset, which seems to help as well as pain killers for the pain that doesn't go away when the spasms do. Just wondering if anyone out there has ever experienced this kind of "episode" and if it's been diagnosed. I am starting to think I am crazy! I have tried googling the symptoms, etc but I can't find anything related to what I am going through! Any help or thought would be appreciated! I was supposed to call 911 and go to the ER at onset of the next episode, but given the symptoms it's almost impossible.