I've been dealing with stomach pain and heart palpitations for a long time. I'm six months into my latest episode, with other episodes in the last five years lasting a month or two at a time. For me, it turned out to be gastritis and acid reflux. While both are quite unpleasant and worth seeing a doctor for, neither is life-threatening in the slightest, and both can easily be caused by anxiety.
My anxiety and digestive system seem to be more in-tune with each other than most people's, so a big and/or unhealthy meal can make me feel pretty bad - stomach pain, heartburn, acid reflux, rapid heartbeat, even shortness of breath when I get bloated enough.
I recommend eating smaller, healthier meals more often throughout the day. You might also want to stock up on chamomile tea and your choice of antacid. Try doing some light exercise immediately after eating a small and healthy meal. Your body will do a better job of starting up the digestive process if you move around a bit after eating, as opposed to just sitting around afterward.