(ABC News) -- An intense scare can do more than elicit a good scream; it can physically affect the body as the neurological system releases intense chemicals in response to a threat.
For most the response to a fright is more or less harmless, with the body becoming primed to fight or flight its way out of a bad situation.
But in extremely rare cases people have literally been "scared to death" after a surge of adrenaline and other chemicals causes the heart to malfunction.
With Halloween around the corner, we've talked to experts in order to understand exactly what happens when you suffer a good scare.
Blinded by Fear
It turns out you can be so frightened you can temporarily lose your sight or hearing.
Dr. Martin Samuels, chair of the department of neurology at Brigham and Women's Hospital in Boston, said the reaction is part of the "fight or flight" response during which the brain redirects all energy to vital body functions.
"You can have severe a fright [that] can cause any part of your nervous system to fail," said Samuels. "Why this happen is related to adrenaline-like substances, [they go into the] bloodstream and affect all the organs.
Going White Overnight
There's little proof that a good fright will turn a person's hair white instantly, but there is a condition that makes it appear as though you've gone grey virtually overnight.
People who suffer from telogen effluvium lose older hair follicles rapidly. As they lose hair, grey strands that were hidden and are often newer, become more prominent, making them appear grey almost overnight.
Dr. Joshua Zeichner, director of Cosmetic and Clinical Research in Dermatology at Mount Sinai Medical Center in New York, said the hair loss usually comes three months after a big emotional event.
"It can be emotionally stressful or physically stressful, even such as an infection or surgery," said Zeichner. "The most common situation is post-partum women."
Fortunately the situation is usually temporary and within about a year the hair will grow back. Although Zeichner cautions he "can't guarantee the hair won't come back grey."
For a worst-case scenario there's always the hairdresser.
Moving in Slow Motion
People who have gone through a sudden traumatic event often describe the feeling of time "slowing down" or moving in "slow motion."
Dr. Martin Samuels at Brigham and Women's Hospital said that the slow motion feeling is part of the body's "fight or flight" response, where your brain will only let you focus on a perceived threat.
As adrenaline and other drugs flood the system, they can make a person hyper-focused on the danger.
"It's called a dissociative state," said Samuels. "It's a kind of hypnosis…where your nervous system is focused on one job and everything else is held at bay."
Pale as a Ghost
After being scared, a person will sometimes be described as looking as "pale as a ghost." But it turns out that the phrase has evolutionary roots.
When faced with a threat, the body will instantly start sending blood to vital organs and muscles to help with either a potential fight or flight.
"All of your organs are focused one task and that's to get away," said Samuels, who points out having a rosy complexion wasn't important for our ancestors who were fleeing dangerous animals. "It happens all automatically. You're not aware of it."
Scared to Death
In extreme circumstances, you can even be "scared to death." Doctors say a terrible fright can result in a massive surge of adrenaline that stuns the heart so badly it stops beating.
Dr. Holly Anderson, director of education and outreach at the Perelman Heart Institute at New York-Presbyterian Hospital, remembers one woman who was with her husband when he received bad news about his health.
When the women left the room, she collapsed in the hallway.
"After I had whisked her off to the emergency room and hooked her up to an EKG, I was surprised to see her whole heart had stopped moving, yet she had perfect blood supply to the heart," recalled Anderson, who is also the director of education and outreach at the Perelman Heart Institute at New York-Presbyterian Hospital/Weill Cornell Medical Center. "She was so emotionally overwhelmed about her husband's condition it literally stopped her heart."