A video called Reactions scrutinises the response of the human body to fear, injury and death.  According to the video, this closely resembles human experience when watching a film of suspense or horror.

"When you perceive possible danger, that sensory information is sent through your central nervous system to a region of the brain that works like a switchboard called the thalamus."

The American Chemical Society, which produced the video, explains that fear as an intellectual response alerts the body to perceived danger.

"The thalamus then hustles the signal over to the amygdala using a neurotransmitter called glutamate. Glutamate-based signalling then transmits the emergency to two parts of the brain - the periaqueductal gray and hypothalamus. When the signal reaches the periaqueductal gray, it switches you to a state of hyper-alertness and makes you startled."

This then triggers a physiological reaction where adrenaline is produced and glucose is subsequently pushed into the bloodstream to provide that sudden boost of energy.  This produces the fight or flight response, which is maintained in that situation by cortisol.

A common action to take under stress of this nature is to scream.  A scream is processed by a different part of the brain than regular speech.  This region is the amygdala, which is usually known as the emergency centre of the brain.  A scream may affect the hearer in much the same manner as the screamer is affected by the source of perceived danger. The scream serves as a medium for the individual to share the state of the brain's chemistry. The hearer's fight or flight response may also be triggered.

If the individual is consequently injured, pain-specific neurons transmit this information to the thalamus which dictates the body's response in relation to pain and self-preservation. If the damage to the body is fatal, the heart and the breath stops.  This is the point where the individual is declared clinically dead.

"Your brain on the other hand is still working and recent research has shown that during this period, your brain can actually enter a hyper state of perceptual neural activity. Some even believe this could be an explanation of near death experiences. [But] soon your brain will shut down for good and it's what's known as a biological death the last stop on the slasher train."