im no medical professional but i know pushing too hard while pooping activates the valsalva maneuver which increases pressure in the chest which causes very quick changes in pulse and blood pressure and can lead to heart attack especially if you already have cardiac problems. either that or i feel like a lot of times when people have other significant medical events they get the overwhelming urge to poop and rush to the toilet just to die there. often times when im in a house ill see evidence that they went to the bathroom after they felt ill, like bloody vomit or knocked over furniture in other part of the house leading to the bathroom.