> effects can range from mild nausea and twitching to drowsiness, cholinergic crisis-like effects (low blood pressure, sweating and salivation), auditory and visual distortions, mood changes, euphoria, relaxation, ataxia, and loss of equilibrium (like with tetanus)
> In cases of serious poisoning the mushroom causes delirium, somewhat similar in effect to anticholinergic poisoning (such as that caused by Datura stramonium), characterised by bouts of marked agitation with confusion, hallucinations, and irritability followed by periods of central nervous system depression. Seizures and coma may also occur in severe poisonings.
In Russia, it's instantly recognizable as a poisonous mushroom - it's a symbol of "danger" that's as obvious as a skull-and-crossbones. Here, in America, most people I've talked to don't even know what it is.
I think those kinds of myths are just natural progressions of exaggerations and oral storytelling
There is actually quite a large body of research, going back as far as the earliest scientific literature on psilocybin (and LSD), about this exact thing.
Useful keywords: microsomatognosia/macrosomatognosia (feeling one's own body shrink/grow), Alice in Wonderland syndrome (AIWS), and Lilliputian/Brobdingnagian hallucinations (seeing tiny people or giants).
Besides which, if you ever are so lucky as to try a significant dose of mushrooms, you will probably see for yourself that you've been underestimating their significance in our cultural traditions.
Swedish tradition has it that trolls would replace human babies with their own babies. It does not take a long leap of imagination to to see how this could be used as an excuse for the practice of putting unwanted/deformed babies out into the forest ”for the wolves”. (Disclaimer: I don’t know how common that practice might have been, since it would presumably stem from prehistoric times)