Something really weird happening to my body?

Diarrhea, may be due to something you ate. Caught a intestinal bug. Would be nice if it continues to get a guiac test done. (test for blood) Test kit can be found at pharmacies now or just save a bit of stool and take it in to the clinic. (may need a doctors appointment there) If it turns out positive you should see the doctor anyway. Dark stool can mean blood coming from higher up the GI tract. (suspicious for cancer)