"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."
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.
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."