(CNN) High school teacher Sarah Giddings stayed home again Friday after more online threats and jittery nerves forced her school and others in southeast Michigan to close.
Giddings, 39, comes from a family of educators who -- along with school staff, students and their parents across the nation -- have become unwilling participants in a recurring American nightmare.
The copycat threats have been rising since Tuesday's shootings at Oxford High School, according to CNN affiliates WJRT and WXYZ. A 15-year-old sophomore is accused of fatally shooting four students in the halls of the Oakland County school -- about an hour from where Giddings teaches English and social studies.
It was the deadliest at a US K-12 campus since 2018 and the 32nd school shooting since August 1, according to a CNN tally.
"It sometimes does feel like we're just lurching from one crisis to the other and we're in this constant state of anxiety," Giddings said.
Legions of teachers, school administrators, staff and students have been emotionally scarred by rampages that -- according to the authors of a new book on mass shootings -- have become "routine events in our lives."
"For the younger generation, it is even worse," psychologist Jillian Peterson and sociologist James Densley wrote in "The Violence Project: How to Stop a Mass Shooting Epidemic."
"Born during the first few years of the twenty-first century, the youngest Americans, from high-schoolers on down, have never known a world without mass shootings," according to the book, which published in September.
"More than half of American teenagers worry about a shooting at their school, and a lifetime of active shooter drills, locker searches, and locked school doors has engendered in them an overwhelming fear of imminent death."
The short- and long-term psychological impact goes beyond the shooting survivors and people left grieving the dead.
"What's really overwhelming is just how big the ripple effects from these types of shootings are -- just the number of people that are impacted," Peterson told CNN. "And for some of them it's lifelong."
Oakland County Sheriff Michael Bouchard echoed those sentiments during a press briefing Saturday, when asked by reporters how the sheriff's deputies who responded to Tuesday's shooting were fairing.
"I was at the scene when there were still children there that were deceased," he said, "but those that were going in there when it was happening, and they were having to go past them, devastating."
Bouchard said specialists were flown in to help responding deputies cope with the bloodshed they witnessed.
"They'll never be the same," Bouchard said. "I told them that we need them to heal for themselves, their family and the community, but we also need them back out on the front line."
Ethan Crumbley has been charged as an adult with terrorism, murder and other counts in Tuesday's shooting north of Detroit that also left seven people wounded.
Crumbley's parents, in a rare move, were each charged with four counts of involuntary manslaughter. The couple pleaded not guilty on Saturday, hours after an hours-long search led to their arrest in a Detroit warehouse.
James and Jennifer Crumbley were criminally negligent and contributed to a dangerous situation that resulted in the four deaths, according to Oakland County District Attorney Karen McDonald.
James Crumbley bought the gun four days before it was used in the shooting, McDonald said. Ethan Crumbley was with him and later called the semiautomatic handgun "my new beauty" on social media. Jennifer Crumbley called the gun her son's "new Christmas present" in her own social media post, according to McDonald.
Prosecutors said in court that surveillance video showed Crumbley with a backpack, then a minute later leaving a bathroom with a gun in hand. He began firing as students ran for cover.
The rampage claimed the lives of Madisyn Baldwin, 17; Tate Myre, 16; Hana St. Juliana, 14; and Justin Shilling, 17, according to officials.
"It's like the same nightmare plays out over and over and over again in the exact same way," Peterson said. "It's so hard to watch."
Tuesday's horror was chillingly similar to previous tragedies.
Aiden Page, a senior, told CNN he heard two loud bangs. His teacher, who was in the hall, ran into the classroom. A bullet pierced a desk the 17-year-old and other students used to barricade the door. This was no drill, he knew.
"I was like, OK, this is a shooter," he said.
"We grabbed calculators," Page added. "We grabbed scissors ... just in case the shooter got in and we had to attack him."
Peterson and Densley built a comprehensive database of mass shooters known as The Violence Project. Based on interviews with perpetrators as well survivors and victims' families, they wrote:
We've turned off the lights and practiced throwing our makeshift weapons — chairs, sharpened pencils, staplers, textbooks, binders, canned goods...
Many of the younger students cry. The older ones will text their last good-byes to their parents, who, in return, will flood the principal and the police with frantic calls. Then, when it's over, it's back to your regularly scheduled programming, like nothing happened.
Page said some classmates cried. Others tried to lend support. They cowered behind desks. A teacher who ran in from the hall when the shooting started called the cell phone of a student in her classroom, where a teen had been shot in the leg.
"The very first thing in my head was, 'This is actually happening,' " Page said. "I'm going to text my family to say I love them just in case I were to die."
He added, "It's definitely going to be weird coming back [to school] especially knowing that people have been injured and ... there are a few students who have died."
Peterson and Densley wrote that "emotional reactions to mass shootings are dulled by repetition. Daily tragedy becomes ambient noise until, eventually, we grow numb to the pain."
For JaVon Pittman, 17, the trauma is still too fresh. He hid under desks with classmates on Tuesday after they barricaded the door with a table and shut off the lights, he told CNN.
"Is this a dream?" he remembered thinking. "We're all just asking like, 'Is this a drill?' "
His younger brother, Jonte, was at the school but managed to escape. JaVon sent him a text message: What's going on?
"It's a shooting, an actual shooting," his brother wrote back, according to JaVon.
JaVon then called his father, JaMar Pittman. He whispered on the phone what his brother had reported.
"Somebody's here shooting up the school," JaVon added.
"Stay calm ... I'm on my way there now," his dad responded.
The lock down, of course, would prevent their reunion for a time.
Feelings of guilt took over.
"You try to be there for your kids," JaMar Pittman said. "You can't be there for your kids, and you get nervous. And for you to be their leader, their father, the superhero, whatever. You can't save your kids. That's devastating."
His wife, Vontysha Pittman, said she tried to stay strong.
"That's just a horrible feeling to know that we as parents couldn't do nothing for them at all but pray," she said last week, breaking down.
"I have to try to be calm for them," she said. She's grateful her sons are home. "There's some parents [where] that room is going to be empty."
Javon also broke down as he remembered close friends Shilling and Myre, who were fatally shot at the school. They were like brothers to him, he said.
McDonald, the county prosecutor, addressed last week the one count of terrorism causing death against Ethan Crumbley -- a rare charge for a school shooting.
"Like every other child that was in that building ... we must have an appropriate consequence that speaks for the victims that were not killed or injured," she told CNN. "They were affected. How do they go back to school?"
Many students can't eat or sleep, McDonald said.
"Their parents are sleeping next to them and we shouldn't ignore that," she added. "There are obviously four children who were murdered and many others injured but over 1,000 were also victimized as well."
The psychological trauma as well as the sense of guilt and loss can be lasting.
"There is a lot of kind of processing and grief work and mental health care definitely needed for that school and community," Peterson said.
"There certainly will be kids with" post-traumatic stress disorder. "It impacts everyone differently, depending on your past experiences and your own coping mechanisms and your own psychology."
Most communities never completely move on from the tragedies, Peterson said.
"We pretend that we do... The public consciousness around these events gets shorter and shorter I feel like... If you don't have kids in school or if you're not a teacher, a lot of people don't realize how bad it's gotten and how much weight we are putting on our children to kind of fight this battle for us."
Giddings, the teacher in Washtenaw County, said her husband, Daniel, and her twin sister, Kelley, also teach. Remote learning along with fights over mask and vaccine mandates have had a heavy toll on educators.
"We couldn't predict a global pandemic but we can predict what happens when a teenager brings a gun to school. We can and should do better," her sister wrote in social media post.
In another post, Giddings' twin wrote: "Sleepless night as I tossed and turned with thoughts of Oxford HS on my mind. 20 minutes away. I know friends & families who work & live there as do most of my students. Being a teacher in 2021 is.....a whole mess. This is not okay."
Giddings said the shootings delivered "one of the biggest body blows in terms of social and emotional stress" during an already difficult school year.
"So many teachers are in the role of advocates and ... allowing students to vent and trying our best to make students feel safe and that takes a lot of emotional bandwidth," said Giddings, a teacher for 15 years.
"We have colleagues, friends that are working there," she added, referring to Oxford High. "And it was hard to not only sleep but it's also hard to talk to my own kids about it."