Like a lot of you, in the weeks since two bombs exploded at the finish line of the Boston Marathon, I’ve watched a lot of coverage on TV, read everything from first hand accounts to op-eds, and talked with countless people about their experiences.

And I’ve noticed, as people have sought to describe and explain what they saw – and felt - during that anxious week of April 15th, there is one word that I hear – again and again: Surreal.

If that word was on the tip of your tongue, too, you weren’t alone.

Peter Sokolowski is editor-at-large for dictionary giant Merriam Webster. He tracks the words people look up online in real time. The data is often something of a bellwether, providing insight into the mood of the country.

By marathon night, some five hours after two bombs rocked Boylston Street and put the entire region on edge, that mood was clear.

"At 8:00 that evening we saw tragedy first, then shrapnel, terrorism, casualty, victim, atrocity, terror, and surreal," Sokolowski said. "So we found that the words that were looked up in the immediate aftermath such as casualty and shrapnel were later joined by surreal as people began to process this event."

That processing was interrupted on Friday, when events took a series of unimaginable, violent turns: A police officer assassinated, A car chase along the Charles. A pre-dawn firefight in usually tranquil Watertown. And a manhunt that turned one of the country’s busiest metropolitan areas into a ghost town.

Sokolowski, watched as the word surreal spiked through that day.

"By the 19th we saw the words terrorism and Chechnya being the top lookups in the news lookups and surreal was number three," he said.

It also mirrors what’s happening in our brains on a level deeper than language.

"I think reaction arises from this juxtaposition of something that’s novel and very emotionally evocative against a context of familiarity," said Richard McNally, a professor in the Department of Psychology at Harvard.

Familiar: Boylston Street. A Crime Scene. Novel: Entire blocks of Boylston cordoned off, damaged, frozen in time, being combed over by authorities in white hazmat suits and blue rubber gloves.

The key here, that thing that is triggering that sensation of the surreal, is the novelty. All of the elements in the scene are familiar to us, we’ve just never experienced them together.

So why is it that we’re seemingly hardwired to respond so viscerally to a novel experience?

"Novel stimuli are likely to be important ones and - of course- potentially dangerous ones as well," McNally explained. "And certainly attending to these things, having all of your attention captured by it, having an emotional response that mobilizes your whole mind and body, so to speak, makes sense because many novel things will be dangerous."

Like explosions at a marathon. A gun fight in a peaceful suburb. And an entire metropolitan area on lockdown.

And McNally says that the fear that accompanies dangerous situations can also contribute to a sense of being in a dream.

"Many times when a person experiences an unexpected, terrifying, life-threatening event, they may feel as if it were not real," he said. "They may feel sometimes even disconnected from their body. Feeling de-personalization, feeling de-realization as if it were in a dream."

From his standpoint, it makes all the sense in the world that people were using the word “surreal” to describe their experience.

"I think these are the psychological variables that are playing a role," McNally said. "How precisely these are substantiated in networks of the brain is another matter. I’m sure the amygdala is involved."

The amygdala?

"The amygdala is a round ball of nerve cells, and it's connected to a circuit in the brain, and we think that it generates the emotional responses that people will get in response to some event which startles them or upsets them," said Dr. Matthew Fink, chief of neurology at New York-Presbyterian Hospital/Weill Cornell Medical Center.

Networks of the brain are his stock in trade. He says that from a neurophysiological perspective, the brain makes no distinction between the real and the surreal - or even the unreal.

"If your brain perceives something that it thinks is a life-threatening danger, whether that’s real or not, it will react in the same way," he said. "Perception and reality then become the same as far as your brain is concerned."

In this case, there was a life-threatening danger. One Fink described as “frighteningly real.” And it’s something that sets off a dramatic chemical reaction in the brain.

"The sympathetic nervous system becomes activated, and the brain releases hormones – cortisone, epinephrine and norepinephrine, what we know as adrenaline, and the result is your heart begins to race, your rate of breathing goes up, you break into a sweat, you might start shaking all over, and so that’s what happens and it happens instantaneously," he said.

And can last anywhere from a few minutes to more than an hour. For most of us, that intense chemical reaction will have no real, lasting effect.

But for the families of those who lost their lives, the victims who were injured, and those who witnessed violent events that week, it will be a longer road.

"There’s a big difference between being present when the event actually occurs and you're there live, as opposed to seeing it on television," Fink said.

Fink says that some could experience post traumatic stress disorder, where the brain pathologically relives that moment of fear and initiates that intense chemical chain reaction - again and again.

In the end, if there is some note of hope for those victims, we find it in that same novelty that helped induce that seemingly universal sense of the surreal.

Yes, the events on Monday, April 15 were violent. They were destructive. They were terrifying and warlike. But they were isolated. They were incongruous. They were out of the ordinary.

And in the moments after the bombs exploded – and in the weeks since – you haven’t had to look far to find elected officials, law enforcement, survivors, families of the slain, doctors, nurses and ordinary people, taking actions, large and small, to keep it that way.

Fink says that’s an environment that bodes well for healing.

"As opposed to, for example, soldiers who are fighting in a war in a hostile population, the people that were injured up in Boston were surrounded and supported by good friends and family members, and just the general population was extremely supportive," he said. "And that is a good result for them, so I think that’s the only good part of the story."

A part that is - thankfully – just as real as the tragic events that started it all.