system
Given the following post, respond as if you're commenting on Reddit:
human
When a person is shot in the head, do they feel pain? How instantly do they die?

Morbid question, but I've always been pretty curious. Hollywood is ridiculously inaccurate when it comes to guns (and everything).
gpt
Anesthesiologist and Pain Specialist here.

Actually, with head trauma, severe pain is TOTALLY possible, but it isn't your brain, it is a result of increased ICP and thus direct pressure on the cranial nerves. This is in addition to the damage sustained to the surrounding tissue. This is assuming a minimal level of consciousness. One poster has suggested pain is a higher order function, in reality, the more accurate answer is the perception OF pain is higher order, being that pain indicators are observable even in some insects, and would obviously be advantageous evolutionarily.

Death is a bit more tricky to explain though, as brain dead(read: dead) patients are often kept ventilated for social(e.g. wife wants to see husband one last time...) reasons, or organ donation(actually, often both). A brain-dead individual has no clinical evidence of brain function upon physical examination. This includes no response to pain and no cranial nerve reflexes.  Note that brain electrical activity can stop completely, or drop to such a low level as to be undetectable with most equipment. An EEG will therefore be flat, though this is sometimes also observed during deep anesthesia. 

A declaration of death can be made based on observations(decomposition for example), or 1.5-5minutes of asystole(flat-line). It is actually pretty hard to explain medically, and certainly ethically. 


Also, some posters have asserted you die via bleeding out, they are on the right track, but not entirely correct. To be simple, your brain is likely to swell following trauma and this can damage areas of your brain, there isn't much room for it to move around, either. Hypoxia is the most common for sure, but hepatic failure is another example of how one might die from head trauma.

So, as someone who has "called time of death", It totally depends on the wound, med/surgical intervention/response time/a hundred other variables, and frankly, I'd be uncomfortable answering this from purely a ballistics stand point, as it quickly enters the realm of things we simply can't generalize. 


This doesn't even touch referred pain...