Shamans, particularly in Siberia and parts of Northern Europe, have historically used the fly agaric mushroom (Amanita muscaria) for its psychoactive properties during rituals and ceremonies. This mushroom was believed to facilitate spiritual experiences and communication with the divine, although its use varied among different cultures and was often accompanied by specific preparation methods to reduce toxicity.
That mushroom is edible, it needs to be decarboxylated first obviously.
Because diarrhoea and vomiting can kill you.
It's called dehydration, eventually you shit and vomit all the water out of your body and that's what actually kills you.