Imodium effectively paralyzes the intestine. Not a go-to remedy. My doctor guided me back to pepto-bismol brand in USA, but any bismal containing concoction wherever you may be). Standard dosage to start, double in an hour if not okay, and then double again as necessary. After that, and nothing works you need a doctor. One time in Bangkok. nothing worked to cure explosive bouts, so to speak. After emptying out, I took a taxi to BNH, emergency. They put me on intravenous fluids and antibiotics, within 30 minutes I was well on path to recovery.
A guiding word. I lost a 38 yo otherwise healthy colleague to diarrhea, he was about 18 hours suffering, drinking lots of water but no food. He got up at night, drank some more water, then fainted. . He was driven to a Miami hospital, suffering a heart attack as the car got to the hospital entrance. They used standard emergency procedure, shock paddles, air bag, but he died. The autopsy showed severe loss of electrolytes. Basically, his nerves were firing, but he had limited conductivity to the heart muscles. Parents know, rush a child to the hospital if they show 10% weight loss. It's an adult problem too.