The Kentucky doctor forcibly dragged off a United Airlines flight in an incident that went viral gave his first interview since the 2017 episode, detailing what he said is the lasting impact on his physical and mental health.

Dr. David Dao spoke to ABC News and said after watching the video for the first time, “I just cried.”

A video screengrab shows passenger David Dao being dragged off a United Airlines flight at Chicago O'Hare International Airport in this video filmed by @JayseDavid on April 9, 2017. @JayseDavid / Reuters

In the video, Dao declined to get off the overbooked United flight, and Chicago Department of Aviation officers dragged him off the plane. Passengers on the Chicago to Louisville, Kentucky, flight recorded a bloodied Dao being violently removed from his seat.

Dao, who is Vietnamese-American, told ABC News that after he hit his head on the plane’s low ceiling, the rest of the encounter is blurry. "After that, to be honest, I don’t know what happened," he said.

Next thing he knew, Dao said, he was in the hospital, with a significant concussion, missing teeth, and a broken nose. Dao told ABC News recovery was "horrible," saying he had to learn to walk again and was put on suicide watch.

Before the incident, Dao said he had run upwards of 20 marathons. Now, he struggles to run just three miles, and has difficulties with balance and concentration.

Attorneys Thomas Demetrio and Stephen Golan hold a press conference with Crystal Dao Pepper, the daughter of Dr. David Dao, on April 13, 2017 in Chicago. Scott Olson / Getty Images

Despite the painful and traumatizing ordeal, Dao said he doesn’t regret refusing to leave the seat because it caused United to review its policy, something Dao said made the incident “positive.”

“Everything happens with a reason,” he said.

Dao settled with United Airlines in 2017 for an unknown amount.

After the incident, United Airlines originally characterized Dao as "disruptive and belligerent." The airline then reversed course.

"Flight 3411 was a defining moment for United Airlines and it is our responsibility to make sure we as a company and all of our 90,000 employees continue to learn from that experience," the airline said in a statement to NBC News Tuesday.

"The changes we have implemented since that incident better serve our customers and further empower our employees," United continued.