A teenager thought her consistent coughing was just a sinus infection. Little did she and her father know it was more than a simple disease.

Most of us treat sinus and flu infections as minor conditions and never bother to seek medical attention. We let our immune system do its work. And with a few over-the-counter pills, we assume we'll get back to normal.

That's what a 16-year-old girl, Shayla Mitchell, assumed when she experienced a stubborn cough that wouldn't go away. She thought it was just a typical sinus infection and told her dad, Tom, to drop her at the clinic for a checkup and then have dinner afterward.

After the doctor's examination, Shayla's condition was worse than they could have ever imagined. She was diagnosed with cancer stage 4, Hodgkin's disease. The infection had caused a big tumor that had destroyed two-thirds of Shayla's chest and one of her lungs.

Things didn't go as they had planned. They hoped to go to a restaurant after the checkup, but they ended up having dinner in a pediatric oncology unit at Fairfax Hospital in Virginia.

Tom revealed:

"We didn't know it at the time, but we would wind up having our next 450 meals in that hospital, as well as hundreds and hundreds of additional meals over the next couple of years."

What they thought to be a walk-in-walk-out session turned to shock when the doctor approached them with a disconcerting face. The look at the doctor's face was clear enough to tell them something wasn't right.

Tom was shocked to break the news to his daughter about her illness. They first went to an American Indian art store and bought two feather bracelets, one for the daughter and the other for him.

Tom knew it wouldn't be gentle explaining to Shayla that she was ailing from a terminal disease. He first wanted to show her daughter that they'll remain connected and go through the situation together.

Tom explained:

"I talked with her about everything and nothing. I talked with her about the wind and about feathers and I talked with her about cancer. We talked about the word 'brave.'"

"We held each other very tight for a very long time. I'm pretty sure we both cried, and we promised each other that no matter what, we would be brave; together we would get through this."

After putting the bracelet on his daughter's wrist, they made promises to each other.

Tom revealed the promises they made with her daughter:

"That I would wear my bracelet until the day she was cancer-free. That for every single night she had to stay in the hospital I would stay with her. That as long as she stayed brave, so would I."

Months passed, and Tom and his daughter spent hundreds of days together in the hospital. She underwent every treatment, including blood tests, radiations, and chemotherapy.

At some point, Shayla suffered heart failure after a chemo treatment.

Tom said:

"Her poor little heart quit working, so they had to install a pacemaker/defibrillator into her chest."

Tom remained with his daughter in her hospital bed. They stayed strong through the unimaginable cancer stages.

One of the toughest incidences happened when Tom was walking his daughter to a car on their way to the chemo clinic. Shayla suddenly began shouting:

"Help me, Dad! IT'S SHOCKING ME! … IT'S SHOCKING ME!"

The pacemaker had malfunctioned and was running electric jolts through her body. Tom held her steady until the shocks stopped.

Tom wrote about the ordeal:

"But I refused to let go. I just held her as tightly as I could and just like that. It stopped shocking her as quickly as it had started, and we rushed to the hospital. It turns out the manufacturer of this device had to recall thousands of them like brakes on a Chevy."

This was one of the several occasions when Tom felt like his daughter was slipping away. But he never let go of her. He held on until the day the doctors said that there was nothing more they could do for Shayla.

That's when Tom felt a complete loss. He didn't know what he'd tell his daughter.

He revealed:

"How in the world was I going to be brave enough to tell my daughter she was going to die. … I knew I had to be brave for HER."

"I did, of course, have that conversation with her, and as unbelievable as this may sound, it turned out to be the most amazing, beautiful, magical, wonderful conversation I've ever had in my entire life, and one that I hope you NEVER EVER have to have."

Sadly, his daughter passed away. Tom will forever remember his daughter's bravery for the rest of his life. Although she lost in the end, she'll remain a hero.