heat damage / heat-related injury can take time to kill someone. this article indicates it can take months. so even a short duration event can kill people, but their heart might not stop until later. substance abuse can also bring it out, as someone experiencing injury may not notice or take whatever small action protect themselves if otherwise impaired. removedpa county (phoenix) keeps a public record of heat-related death and makes reports available periodically, because the impact is unequal across society for reasons you can probably guess (poverty, unhoused, elderly, etc).

something else to be aware of, people can survive heat-injury just by having cool enough temperatures at night. or put another way, the damage from heat-injury during the day can be compounded if the night stays hot as well.

i'm not an expert. i just used to work outdoors, all day in a part of the US that can get high heat and humidity. had a few brushes with heat stress and it comes with its own feelings of mental impairment. like how people succumbing to the cold feel tired and want to rest. heat stress can produce confusion, slurred speech, etc. added danger comes from the disconnect with discomfort and loss of critical cognition.