I found this on a site, in reference to coffee enemas. I wonder if that explains it?
"At the start of the treatment and during “flare-ups,” the bile contains poisons, produces spasms in the duodenum and small intestines, and causes some overflow into the stomach. This may cause feelings of nausea, which could result in the vomiting of bile. If this happens, drinking a good quantity of strong peppermint tea will help wash out the bile from the stomach and bring relief."