First in a series on the Columbine shootings, 10 years later.
At his worst after he survived the Columbine shootings in Littleton, Colo., chemistry teacher Kent Friesen would become physically ill, often throwing up. Now, a decade later, certain triggers can still set off crying jags.
Friesen remembers running past the bodies of two students in the science wing that day as he tried to get help for girls' basketball coach Dave Sanders, who was gunned down and eventually bled to death in the melee.
"I knew he was going to die," said Friesen, who has had to unearth the trauma again as the victims, the country -- and the media -- brace for the 10th anniversary of the most iconic of all school shootings.
On April 20, 1999, Columbine High School seniors Eric Harris and Dylan Klebold, wielding automatic weapons, slaughtered 12 students and one teacher. Another 24 were injured in the 45-minute rampage.
Columbine High School Students, Teacher Report Flashbacks
Though Columbine is now a decade old -- and a larger shooting at Virginia Tech that left 32 dead followed in 2007 -- the wounds of this tragedy are still raw.
A number of books have tried to dissect the motives of the killers and the truth behind the event that played out on television screens across America, but no studies have ever examined the psychological effects of the massacre on those left behind, according to Dr. Frank Ochberg, a former FBI psychiatrist who guided the counseling teams in the aftermath of Columbine.
"There were relatively few who were right at the heart of [the shootings] and were direct post-traumatic stress syndrome candidates," Ochberg told ABCNews.com. "But there were relatively many for whom Columbine was their Gettysburg."
"It changed them, and if they were young, they grew up fast," he said. "Within that group, some are better and some are worse."
Friesen had been holed down in his classroom for three hours that day, with the incessant blaring of the school alarms, exploding pipe bombs and students' screams.
"A gun and holster is the worst one for me," said the 58-year-old, who has retired from teaching and lives in Littleton. "But you live with it. You learn to cope."
Post-Traumatic Stress Lingers
That takes him back to the frenetic day when Special Weapons and Tactics, or SWAT, teams, as confused as those already inside the school, roughed up Friesen, initially believing he was a suspect.
He said the easiest part of dealing with the shootings was getting free counseling for his post-traumatic stress disorder, but many never sought help.
"She saved my life," he said of his counselor. "It was the worst thing I have ever gone through," Friesen told ABCNews.com. "Post-traumatic stress can happen to anybody. It's mind-boggling to know that people still don't believe in it. It's real, and it's one of those things that just won't go away unless you get help."
According to Ochberg, who specializes in treating post-traumatic stress and the effects of violence, "The healthiest thing, hard as it is, is to grieve a loss.
"Grief is good and normal," said Ochberg, the former associate director of the National Institute of Mental Health.
But when distress becomes disorder, post-traumatic stress -- or what was once called "shell shock" or "battle fatigue," is often diagnosed.
PTSD is Medical Condition
"PTSD is when a person undergoes something really traumatic, horrific and terrifying, but their reaction is not proportional," said Ochberg.
"The brain isn't operating the way it should. The equivalent of kidney failure or a ruptured spleen, it becomes a medical condition."
Ochberg helped identify PTSD in 1980, when returning Vietnam veterans and rape victims' advocates and counselors reported an array of symptoms: reliving of the event; avoidance of "normal things that you have an appetite for" -- joy, love and food; and a sense of being always "hyped up."
Treatment should be "collegial," attempting to "normalize" the patient's life, "even though the brain is broken," he said. Educating patients about the disorder, re-establishing eating and sleeping patterns and working with "humor and spirituality," is key.Often, doctors prescribe medication for sleeping, anxiety or depression.
Sometimes Ochberg allows the patient to experience flashbacks in a controlled and safe setting, so eventually they become less debilitating.
"Together, we try to get our arms around it," he said. "You can actually grow from it."
"It says nothing bad about you if you've got PTSD," said Ochberg. "That's what you got. You were in the fire and got burned. Some people deal with burns better than others."
Shooters Paralyzed Teen
Such was the case with Anne-Marie Hochhalter, who got shot in the chest and was permanently paralyzed from the waist down. Eighteen months after the massacre, her mother committed suicide and an experimental treatment to try to help her walk again failed.
Now 27, Hochhalter said she has climbed out of a "dark hole" and has forgiven the shooters.
Today, after four surgeries, Hochhalter, Columbine's so-called "miracle girl" has a degree in business management and is a part-time manager at a local Bath and Body Works store.
"It's not at the forefront of my mind," she said in talking about what she'd endured," she told ABC's Kate Snow in an interview to air on ABC's "Good Morning America." "And it, it helped me, you know, [to] believe in faith as well that I'm here for a reason. ... I have a lot more to give to the world."
"I've tried to move on, you know, with my life. But I do think about it sometimes, with the anniversary coming up."
But like other students and teachers who survived the shootings, flashbacks still persist.
Nail Polish Sets off Flashbacks
Hochhalter said the smell of nail polish or formaldehyde can set her off, reminding her of her recovery in the hospital, where doctors stitched up a hole in her vena cava, a pair of veins that deliver blood to the heart, and literally glued her liver back together.
Automobile "backfirings are probably the worst, and fireworks," she said. "I can't do fireworks at all.
Others haven't fared so well, and the fallout of Columbine has sent them on a downward spiral.
At 16, Mark Taylor survived a barrage of rapid-fire bullet wounds (somewhere between six and 13), but the years that followed have been tough. Today, Taylor lives with PTSD and mental illness, according to his father, a janitor who lives in Denver.
"For about two years, he was doing really good," Mark Taylor Sr. told ABCNews.com. "Then he had a mental breakdown. He used to be normal, and now it's almost like talking to a blank wall."
Taylor, who was once close to his son, has not talked to his son in months. Young Mark and his mother live with a relative in Espanola, N.M., surviving on food stamps and disability income. When ABCNews.com talked to Mark, his speech was slurred and incoherent. His mother, Donna Taylor, was equally distraught. "We are living like gypsies," she said.
"I need help so much," she told ABCNews.com, intermittently coughing and crying. "I'm so scared. He's almost choked me several times. He cannot think logically anymore."
Mark could only manage to say, "I don't want to talk about it anymore. It's America's guilt."
His father described Mark as "paranoid and delusional," and said mental health officials diagnosed his son with a genetic bipolar disorder that was exacerbated by the trauma of Columbine.
Mark, whom police referred to as "dead kid walking," was hit when the killers aimed at students sitting on the grassy knoll adjacent to some steps. He fell to the ground and played dead while three others escaped uninjured.
'Bowling for Columbine'
He spent 36 days in the hospital and was tutored during his convalescence but never graduated from high school. "It was pretty horrific," said his father. "Basically, you're in shock."
After the shootings, Mark participated in the making of Michael Moore's 2002 anti-gun documentary, "Bowling for Columbine," and wrote a book about his inspirational recovery, "I Asked, God Answered: A Columbine Miracle."
The book logged some sales early on, but Mark was "not in a state" to promote it, said a spokesman for Tate Publishing, which released the book in 2006.
Donna and Mark Taylor, who have six other children, divorced in the aftermath of Columbine. Their son experienced several mental breakdowns and was hospitalized three times, according to both parents.
Mark's mother believes the antidepressants doctors prescribed were "killing" her son, and she took him off all medications. In 2006, they began a three-year odyssey moving from Colorado to Kansas City to live with friends. For a while, they were living in a homeless shelter in Buena Park, Calif.
Shooting Victim Too Sick to Work
Today, the 26-year-old is too sick to work and has only a Lexus to show for the estimated $185,000 he received from the Columbine victim's fund.
"He blew it all," said his mother. "It's hard to control someone that age."
Like the rest of the nation, 10 years after Columbine's massacre, Donna Taylor "cannot let this thing go," said her ex-husband.
"The mere fact is that guns aren't the only problem," said Donna Taylor. "Life is so full of darkness. School should be the safest place, not the most dangerous place for your child."
Retired teacher Kent Friesen has channeled his own grief into the plight of returning Iraq War veterans, many of whom suffer from post-traumatic stress.
"I am passionate about this," he said.
A 2007 American Psychiatric Association survey of soldiers showed overall prevalence of PTSD was 16.6 percent. But 31.8 percent of those wounded or injured reported having the disorder.
Today, Friesen cannot talk about the veterans without breaking down. "I admire those men," he said. "I hope they get the help that they need."
These days, he finds solace making furniture in his workshop and volunteering for a church youth group. Friesen cannot view violent movies without crying, but he relies on the patience of his wife and two sons, 30 and 32, to steer him clear of emotional triggers.
"I will put this [interview] on a back burner and deal with it later," Friesen told ABCNews.com. "I probably won't sleep well tonight. The thoughts and things race in my mind.
"But that's OK," he said. "That's what I have to do. I don't want to bury it, and my release is my tears."
Next: The Columbine Shootings, 10 Years After: Portrait of the Killers
ABC's information specialist Nicholas Tucker contributed to this report.