Please explain why is it risky to administer physostigmine to all patients presenting with muscle weakness?

Bad idea: Physostigmine is a powerful drug with many nasty side-effects. The vast majority of people presenting with muscle weakness do not have undiagnosed myasthenia gravis or anticholinergic poisoning. Give it to somebody heat exhaustion and you'll further mess up the electrolytes. Give it to some who's having a stroke and they may throw up and aspirate. Botulism / neuropathy? It can kill them.