For 55-year-old U.S. Army veteran Sae Joon Park, this was the hardest moment of his life. Not getting shot in combat. Not the years battling post-traumatic stress disorder or addiction. Not prison. It was leaving the U.S., a country he called home for nearly five decades.

On Monday, Park, a green-card holder, self-deported to South Korea. His removal order was the result of charges related to drug possession and failure to appear in court from over 15 years ago — offenses that, he said, stemmed from years of untreated PTSD.

Park's story reflects both the challenges of life after combat and the perils that noncitizen veterans face if caught in the legal system — realities made harsher amid the Trump administration's push for record deportations.

" I can't believe that this is happening in America," Park told NPR in an interview prior to his departure. "That blows me away, like a country that I fought for."

U.S. Immigration and Customs Enforcement did not immediately respond to a request for comment.

"I realized I was shot"

Park came to the U.S. from South Korea at age 7 to join his mother in Miami. A year later, the pair moved to Los Angeles, where Park would spend the rest of his childhood.

Growing up, Park said he didn't have many positive influences. But he looked up to his uncle, a colonel in the South Korean military. After high school, Park enlisted in the U.S. Army.

"I wanted direction and [to] better myself and maybe help serve the country," he said.

When 20-year-old Park finished basic training, he was deployed to Panama — unaware that he would soon be part of the 1989 U.S. invasion known as Operation Just Cause to topple Manuel Noriega's regime.

One afternoon, while eating lunch with his platoon, Panamanian soldiers began to fire, according to Park. He started shooting back when, suddenly, he felt a sharp pain in his back.

"I realized I was shot," he said. " So I'm thinking, 'Oh my God, I'm paralyzed.' And then thinking, 'Oh my God, I'm not just paralyzed. I'm dying right now.'"

Park was flown back to the U.S., honorably discharged, and awarded a Purple Heart. Though his body began to heal, he said his mind did not.

" I was suffering from PTSD severely," he added. "From sleeping nightmares to like, having just fearful thoughts all the time. Couldn't watch horror movies, couldn't hear loud noises."

Back then, Park didn't know he was dealing with PTSD. So, he never sought help and the trauma slowly took a toll. He eventually turned to drugs to cope.

" I had to find some kind of a cure for what I was going through," he said.

Throughout his 20s and 30s, he battled a crack cocaine addiction. One night in New York, while meeting up with a dealer, police appeared and arrested Park. Later, he skipped one of his court hearings.

"I just couldn't stay clean," he said. "So finally when the judge told me, 'Don't come back into my court with the dirty urine,' which I knew I would, I got scared and I jumped bail."

Park was charged with possession of a controlled substance and bail jumping, which derailed his chances of naturalization or getting relief from a deportation order.

Park said for a long time, citizenship was not a priority because he did not fully grasp the consequences of remaining a noncitizen. Although the U.S. offers expedited naturalization for those who serve honorably in the U.S. military for at least one year, or a single day during wartime, Park was discharged before he had served 12 months and the invasion of Panama was not classified as a period of hostility.

"I have to accept the fact that this is probably the last time I'll see her"

Park was in prison for three years starting in 2009. Drugs were easily within reach, but he said he lost all desire for them.

After his release, Park moved to Hawaii, where his family was living at the time. He found work at a car dealership in Honolulu, where he spent 10 years while raising his son and daughter. Watching them grow into kind, successful adults was his greatest blessing, he said.

After prison, Park received a removal order but was allowed to stay in the U.S. and required annual check-ins with immigration agents — which is typical for individuals that ICE does not consider a priority for deportation.

That changed earlier this month. At a meeting with local ICE officials in Hawaii, Park said he was warned that he would be detained and deported unless he left voluntarily within the next few weeks.

So, Park booked his flight and spent his final days in the U.S. — playing one last round of golf with his friends, savoring Hawaii's famous garlic shrimp, and enjoying time with his children and 85-year-old mother.

" I have to accept the fact that this is probably the last time I'll see her," he said.

On Monday morning, Park hugged his loved ones goodbye. Then, just like he had as a child, Park boarded a plane all by himself — this time, bound for a country he barely remembers, leaving behind the one he fought for.

"Even after everything I went through, I don't regret joining the military or getting shot," he said. "It's part of my life, my journey. It's made me who I am today."