Fear starts in the brain
Most of us don’t have to think about breathing, digesting our food or making our heart beat. The autonomic nervous system takes care of these functions we think of as automatic. It is divided into two branches: the parasympathetic nervous system (the rest and digest system) and the sympathetic nervous system (the fight-or-flight system).
Fear kicks your fight-or-flight response into overdrive, Evans says. Your adrenal glands secrete adrenaline. Blood flow decreases to your brain’s frontal lobe, which is responsible for logical thinking and planning, and the deeper, more animalistic parts of your brain—including the amygdala—take over.
Like an animal trying to avoid being eaten by a predator, all of your body’s resources get diverted toward one goal: staying alive. Your heart rate and blood pressure increase, you breathe faster and your muscles tense up. Your pupils dilate so you can see the threat more clearly, says Evans.
Some people may get sweaty and flushed or have cold, clammy hands when they’re afraid, he says. That’s because the blood flows away from the edges of the body toward the larger, interior muscles.
“If you’re going to be fighting or fleeing, you want as much blood flow to the big muscles of the body,” says Evans.
You’ll also experience a decrease in digestive activity. Peristalsis, which is a wave-like movement in the gastrointestinal system that controls digestion, takes quite a bit of energy, says Evans. And your body does not have time for that when you’re trying to avoid joining the Army of the Dead.
“All of the things that we think of as longer-term interests get diverted to the immediate interest: fight or flight,” he says.
Anxiety is fear gone wrong
The fear response is designed to deal with imminent physical dangers. But we live in a society and at a time when those kinds of dangers are pretty rare, says Evans. Instead, the kind of danger we experience is more psychological or social in nature.
But your brain—which tends to overgeneralize—can’t tell the difference, says clinical psychologist Kari Astley Stephens, Ph.D. That means your brain can react to something like missing a work deadline the same way it would respond to something that’s actually life-threatening, like a car crash or an earthquake.
“Anxiety is an emotional response to something that the brain thinks is dangerous, but isn’t actually dangerous,” says Stephens.
Some of this anxiety can actually be good. It protects you by telling you when there is something coming your way that you need to avoid. For example, missing a work deadline won’t kill you, but it could cost you your job. And walking outside at night isn’t necessarily dangerous, but having the fear response kick in and tell you to walk with a friend could keep you out of an unfavorable situation.
For people who have an anxiety disorder, the response crosses a line where it’s no longer healthy, but is interfering with life, says Stephens. Say that work deadline isn’t for two weeks, but you’re so worried you won’t get the project done that you can’t get anything else done. Or you get so nervous about going out at night that you miss out on social gatherings. That’s when it’s no longer “good” anxiety.
The physical response to anxiety is very similar to fear, says Evans, but usually to a lesser degree. A panic attack, on the other hand, is a “pure fight-or-flight reaction.”
“It’s this amazing process, but if it’s happening when you don’t want it to happen, that’s when people come to see me,” he says. “It’s designed to keep us alive, not to harm us.”