"Bad batch" means one ate mushrooms that aren't psilocybe. I've done that before. When I was a teenager, we gathered our own mushrooms from a cow pasture near my high school and I once made the mistake of picking a few of the wrong species. But they're not going to cause a bad trip, per se. They'll cause physical discomfort and vomiting, and that can in turn cause a bad trip as a result of the emotional distress. But it's not a physiological phenomenon in the sense of being directly neurochemically induced. It's not like the psilocybin "goes bad" and causes a bad trip the way food goes bad and causes vomiting.

In other words, the psychological phenomenon of the bad trip occurs as a mirror image of the physiological phenomenon of the food poisoning. And since vomiting is a common occurrence at the beginning of trips, it's useful to learn to accept that "purging phase" without panicking and spiraling into a bad trip from the fear of potential food poisoning. Just trust your body to be able to process what you've put in it and you'll come out the other side all the stronger. It's important to learn the basics of the science involved with tripping. For example, the physiology of food poisoning and what one's body does to deal with it. Knowledge is power and it will help you overcome fear borne of the unknown. If you go to the hospital, they're just going to pump your stomach and rehydrate you intravenously. It's scarcely different from what you're already naturally going to want to do instinctually, which is vomit and drink lots of water.

And ultimately, if you are actually poisoned, there's not much anybody can do for you. Accept the L and die with grace on the forest floor. It's better than dying in a hospital bed surrounded by cops and moms. At least, that's my personal opinion.