Kyler Baughman seemed to be the face of fitness.

The 21-year-old aspiring personal trainer filled his Facebook page with photos of himself riding motorbikes and lifting weights. He once posted an image of a kettlebell with a skeleton, reading: "CrossFit, hard to kill."

So when he came down with the flu last month, his mother said, he possibly assumed he simply needed some rest.

"I think he thought, 'I just got the flu; I'll be all right,' " his mother, Beverly Baughman, told NBC affiliate WPXI.

Posted by Kyler Baughman on Tuesday, 27 December 2016

But days after Christmas, Kyler Baughman was worse - coughing and running a fever, his family told the news station. They said he went to a nearby hospital in western Pennsylvania and, from there, was flown to UPMC Presbyterian in Pittsburgh.

Soon after, on Dec. 28, Kyler died of "organ failure due to septic shock caused by influenza," his mother told WPXI.

Kyler Baughman, from Latrobe, had gone home for the holidays with "a snotty nose," his mother recalled in an interview earlier this week with WPXI. "We saw him the 23rd for our family Christmas get-together and we noticed he wasn't feeling well," Beverly Baughman told the news station.

The day after Christmas, Kyler Baughman went back to work - he earned a living moving furniture at a local furniture store and unloading goods at Walmart, according to his social media accounts.

But he could not make it though the day.

Olivia Marcanio, who was identified by WPXI as his fiancee, declined to comment to The Washington Post, but told the news station that Kyler Baughman, "just laid down and went about his day, and that was the day he was coughing and said his chest hurt."

Now - not even two weeks after his death - his mother said, "It doesn't seem real."

Each year, as many as 650,000 people die from respiratory complications related to influenza - an increase from the previous decade, according to recent data from the Centers for Disease Control and Prevention and the World Health Organization.

"These figures indicate the high burden of influenza and its substantial social and economic cost to the world," Peter Salama, executive director of WHO's Health Emergencies Programme, said in a news release last month. "They highlight the importance of influenza prevention for seasonal epidemics, as well as preparedness for pandemics."

However, according to the CDC, "most people who get influenza will recover in several days to less than two weeks." Complications range from sinus and other infections to pneumonia and organ failure.

According to Kyler's obituary, he enjoyed "motocross, reading, and going to the gym."

And that's one reason his family is sending this message to others: Listen to your body.

"Try and know your body. Don't let things go," Kyler Baughman's father, Todd Baughman, told WPXI through tears. "Whenever you have a fever for multiple days, don't let it go, get it taken care of."