The vitamins helped you knock it out quick. The Ivermectin (animal version) maybe what gave you diarrhea and stomach issues.
Invermectin is invermectin. Some is made in a more tightly controlled lab or not but it is the same stuff. If you dose correctly and anyone with an IQ over 90 can easily do it. Same stuff, same effects, be it approved for veterinary use of approved for human use. Intestinal tract issues are one of the myriad of Wuflu symptoms. The intestinal issues are almost as prevalent as the taste/smell issues. That said, the Hershey squirts are a possible but rare invermectin side effect.
I took a dose of it (animal version) with a tablespoon of peanut butter just last night. It caused no issues here.