I imagine you're not keen to have same experience again.

Suggestion: tear it up, start doing only rue. Get that right first. Rue should and could give you a telling rue experience on its own, it's not the same of course but it is a way to see where that over the top pain came from. Start low, build up, see if it's the rue.

BTW, how was the rue brew made? Did boiling down volume perhaps concentrated acid to levels where it can hurt you. No kidding, a person had to be hospitalized after he had used phosphoric acid in his washes, collected the washes, reduced volume to a shot drink and got hurt. Phosphoric acid does not evaporate away during reducing like vinegar does, it just kept getting more acidic as the volume dropped. Just telling.

One should also not underestimate how immense hurtful gas in the intestines can be. Blocked gas creating local pressure in the tube, very hurtful. The moment a gas-lock frees itself by displacing, all pain can suddenly be gone as you describe.

I hope you get to the bottom of this.

Just sprouting some ideas here.