Ever had someone make you jump and find yourself clutching your chest? It's like something just zapped behind your sternum, you feel a little shaky even. You lean against the wall as you recover, wondering why your friend is such a jerk, and why you can physically feel it in your chest when you get a fright.

When we write about fear in fiction, phrases like “heart-stopping” often get thrown around, but the science of fear tells us this isn’t what’s happening, quite simply because it wouldn’t make any sense. When we get scared, the sensation we’re feeling is all to do with preparing ourselves to tackle an oncoming threat, and cardiac arrest wouldn’t get us very far if we were being chased down by a lion.

What happens when we get a fright?

If something makes you jump, it activates what’s known as the sympathetic nervous system. It’s an internal tool that basically prepares us for the fight or flight response by releasing certain hormones and influencing our physiological function.

A key ingredient is adrenaline (epinephrine) that gets squeezed out by the adrenal glands into the blood. This causes a pretty instant reaction from the cardiovascular system as the heart starts pumping faster, delivering more blood to your organs and muscles. That’s because they’re going to need as much oxygen as they can get if you’re about to leg it from a predator.

How does adrenaline make you feel?

As anyone who has ever had to use an EpiPen will tell you, a sudden rush of adrenaline isn’t a good feeling. As a stress hormone, it brings on feelings of nervousness and anxiety similar to how you might feel if you were about to do a bungee jump, and a rush can be a symptom of PTSD when thinking about traumatic incidents from the past.

We use adrenaline as a medicine because it can have a positive influence on people experiencing a medical emergency. It’s effective for anaphylaxis brought on by exposure to an allergen like peanuts because it can open the airway. It’s also used in certain cases of cardiac arrest because of how it influences the strength and rate of heartbeats.

Shakiness, rapid pulse, and chest tightness are all part of the unpleasant symptom set for a sudden surge in adrenaline. Add to that increased alertness and you become suddenly very aware of the changes in your body, and this becomes all the more noticeable in a scenario where you’re not actually in danger – such as your mate jumping out at you when you thought you were home alone.

It’s important to note that while sympathetic nervous system activation is a normal response to a surprise, certain heart conditions can be triggered by fright. Anyone experiencing chest pain or ongoing discomfort should contact their medical practitioner. After all, it is theoretically possible to be scared to death.

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.