After I eat, I feel very dizzy, to the point of almost blacking out, tachycardia and weakness. My Dr. said this is "Dumping Syndrome"; my pyloric valve opens and closes rapidly, after eating; completely emptying my stomach, which causes dizziness, because of low blood sugar, then my body releases glucose; I have such severe stomach (not abdominal) pain; horrible spasms, which double me over....Bentyl did not help; made the spasms worse...so I am on Xanax (0.5 mg every four hours to stop the pain from the severe spasms) which is an anti-anxiety drug; but, it does the trick...stops the horrendous painful spasms.
I have rapid gastic emptying which causes rapid heart rate. Usually people who have had surgery get it which I never had so is not the case for me. If that was the case you would have other symptoms to go along with it. It's extremely uncomfortable.