It was the "perfect storm," Jim Flath says of his 26-year-old son's sudden death during a family ski vacation in Colorado. His youngest son, James, died Sunday -- one day after he was diagnosed with the flu.

"It was a really unfortunate series of events," Flath, of Lee's Summit, Missouri, told Fox News. "The flu combined with high altitude sickness ... and he had sleep apnea, which may have caused some of the problems."

Feeling under the weather, James went to a nearby urgent care Saturday morning. Doctors told him he had the flu and to take it easy. His parents and his girlfriend planned to go out to dinner that night, but James decided to stay behind and rest in the condo, hoping he would recover quickly.

"He said, 'Go have fun!'" Flath recalled. "I don't think he or us realized how sick he was."

So, they left for a short period of time and returned to find James unresponsive.

"James loved life. He always liked doing things for other people and rooting for the underdog." — Jim Flath

"He was breathing but we couldn't revive him," Flath said.

The man's family and friends were devastated by the news of James' death. But Flath said they had to do something -- they couldn't just sit around being sad.

"We're sad, obviously," Flath said. "But James loved life. He always liked doing things for other people and rooting for the underdog."

In order to celebrate the life James lived, his family started a social media movement called “Giver 4 Jimmer." The idea is to inspire others to pay it forward with acts of kindness -- whether it's paying someone's bill or carrying someone's heavy shopping bags.

"Everyone is angry at each other and if we can do something to help people be a little less angry and kinder to each other then why not?" Flath said.

With help from two of James' friends, who work in social media, Flath created a Facebook page for the movement. More than 900 people have already followed the page.

The family even created "Giver 4 Jimmer cards" for people to pass out after they've done an anonymous good deed. The bright green cards encourage others to follow suit.

Dozens of people across the country -- from San Francisco to New England -- have already shared their kind acts in honor of James with the Flath family.

"Paid for the woman’s groceries in front of me today," a woman from Kennedy, Texas, posted on the page Tuesday. "Wasn’t much but with tears in her eyes thanked me and told me how much it helped because her husband has cancer and they were struggling with their money."

"I saw this today and even though I am unemployed and financially struggling this year, I had a friend even worse off than I am," another man from Seattle explained. "So I anonymously went in and made a car payment for him ($212) so that he would not lose his car."

Reading about people's kindness warms Flath's heart.

"If we make some people's lives better, that's obviously a huge bonus," he said.

Flath recalled a time his son paid for a father's meal when he noticed him "struggling" at breakfast with his young daughters. He also remembered how James would never forget to bring money with him to the gym so he could give homeless men who sat outside an extra buck or two.

"When he gave them money they'd pump him up and tell him how strong he looked. He'd brag that he has to buy his compliments," Flath recalled James joking.

Even with the positive response on social media, Flath admits it's impossible not to feel sad about James' death. The 26-year-old was supposed to be the best man for his brother's destination wedding in April.

But whether he has good or bad days, Flath plans to keep the movement alive for as long as he possibly can.

"I don't plan on ever shutting it down. I'll have cards in my wallet forever," he added.