That is weird. Also, the hypothetical doesn't really make economic sense. We're all around 24-48 hours from death if we don't eat and drink, and yet the market has no ability whatsoever to exploit that fact because competition is too powerful.

An antidote-seller (chemist) who was known for charging more when you needed medicine would get wrecked in the market competing with a chemist who just sold stuff to whoever at a known price. Not to mention that anyone could buy from the chemist in the good times and set up shop just outside selling at stable prices arbitraging the scheme away.

A key reason of why free markets are practical is that it isn't effective to try and segment market based on consumers' raw need. The product needs to be genuinely different for that strategy to have a chance (eg, an expedited service - which is probably going to justify extra cost to someone dying of poison).