I have this happen too. I believe its caused from the vagus nerve getting stimulated causing these symptoms. Even so its a scary feeling.
Thank you. I just don't understand. I've had anxiety since last March, but I've never have had problems with bowel movements. I've had breathing problems, lightheadness or pseudo-fainting, chest pain/tightness, chest/"heart" zaps, muscle jerks, and so much more. I must suffer from some severe health anxiety. Everyone thinks I'm utterly crazy and I never can get help with this. I've had various fears from brain tumor to ministrokes everything! Now I'm afraid of a heart attack or cardiac failure from bowel movements. I had issues with constipation in early childhood, but nothing like this!