You may feel like your dying (been there done that) but gastric pain and diarrhea and constipation are common anxiety symptoms, and I found that when I was trying to raise the dose of Lexapro I was on last year when my latest episode began I had even more problems till my body adjusted. I am still having some setbacks, but my stomach is usually okay, maybe because I take a small dose of remeron at night, it tends to ease the stomach stuff that other meds like the pristiq I am on right now can aggravate. I had an endoscopy recently (was fine) and a colonoscopy about 4 years ago, and it found nothing. Plus I've had an abdominal cat scan with and without contrast last summer b/c I was losing weight, well it is the anxiety that does this to me. When I am feeling better I either stabilize or gain a few pounds, so don't underestimate the power of anxiety to do all kinds of weird things to our digestive systems. FWIW this is round three for me, and I had similar stomach issues along with other physical and mental unpleasantness in the two prior attacks, but I didn't die then (though the panic attacks that heralded the first two episodes but not this one--this time it was just crazy anxiety for days after, oddly enough, some bad abdominal cramping-were very convincing, in fact during the first episode they kept me in the icu for two days after a second panic attack and two more days in the hospital before they released me, and that was a long time ago and I didn't die then and that was 26 years ago). I hope this helps some small bit, I still have my particular HA fears but so many of us have been down this road before, so you are not alone and you will eventually overcome this.