The Science of Fear: What Happens to Your Body After a Good Scare

— -- If you're planning on enjoying a few frightful scares this Halloween, you might want to be sure to take a few deep breaths as well.

Fear can have a direct and noticeable effect on the body, even if you're just heading to a local haunted house or enjoying a scary movie. In the face of a scary event, real or fake, a person's fight-or-flight response can take over, which can result in myriad of changes as the adrenal glands react to fear by going into overdrive, flooding the body with adrenaline.

Dr. Felipe Amunategui, a psychiatrist at University Hospitals Case Medical Center, said in a frightful situation, a person may have an increased heart rate, rapid breathing, and even changed brain activity.

"If you need to fight or flight, you will start to dilate your pupils so you have more light reach your eyes," Amunategui explained to ABC News. "Your blood starts flowing into your large muscle in the extremities, preparing you to take action. This happens in a fraction of a second."

As adrenaline hits your brain, your amygdala -- a small almond-sized portion of the brain -- starts to override your rational reactions, Amunatequi explained. As a result, a frightened person will simply react to a scary situation rather than sit down and rationalize their reaction, for example, to a killer clown at a haunted house.

The response would have helped keep our ancestors alive if they encountered any danger by helping them put all their energy in into fighting or fleeing the danger, Amunatequi said.

"If you [survived] the encounter, you have to dispense with all that riled up energy you have, you end up really jittery," Amunatequi said. "It's designed to keep you alive. You’re going to cash all these chips in to get away," from the predator.

You may think that a fake scare doesn't mean the same response, but Dr. Frank Farley, professor at Temple University and former president of the American Psychological Association, said the reason a horror movie can strike terror is because it relies on your brain making connections between fake and real events.

"We know that there are horrendously awful people out there," Farley said. "It gets into your head and makes all the connections with real life."

Even fake horror can affect people in real life by heightening their senses, Farley said, so that they start to be more afraid even after the lights come up.

"You can be afraid of some sounds or images and have a sense of fear, only because of the connection to real horror that you hear of," he explained.