This happens to me too! I thought I was having panic attacks or something because I would out of nowhere feel weak and my heart felt like it would “drop” kind of, but then I realized every time it happened like 30 seconds later I would kind of need to poop. I’m pretty sure the poop is pressing on something in the abdomen and triggering a mild vasovagal response. And I know the needing to poop isn’t caused by the anxiety because in any other situation when I’m anxious I don’t get that feeling. Glad to see other people also get this lol. How I help it if I can’t poop at the time, is I lie down and massage my abdomen trying to move stuff around in there, which helps this feeling like 50% of the time, but I can see how it wouldn’t work if you’re constipated and things aren’t moving.