PITTSBURGH -- Oddly, Ryan Clark had felt sick to his stomach playing in Denver's mile-high altitude before, as a member of the Redskins three years previously. But after the Steelers lost to the Broncos on Oct. 21, 2007, he was in agony.
The team doctor tilted back Clark's seat on the plane, climbed onto his lap, started pressing around his ribs and asked him to try to take deep breaths. They wheeled him away before takeoff and took him to the hospital.
"If you were able to stick your hand inside your body and punch through your ribs, it would feel like it's trying to come out," Clark said, describing his pain.
Thus began a baffling, sometimes harrowing, three-month odyssey that would take the Pittsburgh safety to the brink of death. When Clark recently leveled Baltimore's Willis McGahee with a brutal -- but legal -- tackle in the AFC Championship Game, sending the Ravens running back to the hospital, it was a haunting flashback for Clark and those who love him.
"When we hit, I think I just kind of blacked out for a second," Clark said. "That's how I've always played. When you think about it, you flinch, and when you flinch, there's a possibility that somebody could hurt you. If you think about what could happen, what could be worse than what I went through last year?
"What could be worse?"
The Steelers' defense is the NFL's finest, in terms of fewest points and yards allowed. And while the lineup is filled with marquee names, according to team statistics the anonymous Clark finished the regular season as the second-leading tackler. As the not-so-free safety, he allows Troy Polamalu to careen randomly all over the field. Clark is, literally, Pittsburgh's last line of defense.
A year ago, that was unimaginable.
Clark was born with sickle cell trait but had never experienced full-blown complications of the disease, in which healthy red blood cells turn sickle-shaped and compromise blood flow in and around the spleen. There are two factors, according to studies, that can cause this: extreme physical exertion and high altitude. Both were present in Denver, but no one understood the ramifications at the time. A week after returning home to Pittsburgh, Clark's condition worsened dramatically.
"Apparently, his spleen was disintegrating," said his wife, Yonka. "It wasn't getting the oxygen it needed to operate. It disintegrated. It melted."
It might have happened the night Clark's mother and his wife tucked him into bed, piled up the blankets and wrapped his head in a scarf. Yonka had the blow-dryer going under the covers to warm him up -- trouble was, he had a fever of 104 degrees.
"They kept telling me, 'It's not cold. It's not cold,'" Clark said. "I was like, 'I'm freezing.' So I started to shake. My mom was laying on top of me, praying, and I'm bouncing the bed, moving the bed.
"That was the only time through the whole process I thought I could die. I even said a prayer. I just asked the Lord to forgive me for anything, just asked his mercy upon my life because I thought that was it."
Clark wondered how his wife and three children would fend for themselves with the head of the family gone.
"You think about you've got a 7-year-old son," Clark said. "What's it going to be like without Dad? You think about your daughters. Who's going to walk them down the aisle? Who's going to take them on their first date, so they know how men should treat them? Who's going to marry my wife after I was gone?"
The immediate crisis passed, however, and, despite spiking fevers and night sweats that drenched his pajamas, Clark tried to go to work each day. Even though he couldn't dress himself and needed a ride to the facility, doctors and coaches were optimistic he soon would play.
"When someone is telling you [that] you should be all right, all the tests check out, you want to feel OK," Clark said. "I'm training, fever is 102, 103. I'm lifting weights. I'm trying my best to walk around the field and people are saying things like, 'Oh, you should be ready Monday or Wednesday.'"
How did that make him feel?
"Angry. I felt like you're not going through this," Clark said of team doctors and coaches. "There's no way I can wake up every morning with a normal temperature, then by 2:30, 3, you have to send me home because I'm 103. I know that's not normal."
Said Yonka, "Certain doctors want it to be what they want it to be. When you find scientists, doctors that have gone to school for such a long period of time, they want to be able to explain everything, and when they're not able to, it just kind of comes down to there's nothing there, that it doesn't exist.
"In this case, particularly, it could have cost my husband his life."
After three weeks on the inactive list, the Steelers placed Clark on injured reserve. In December 2007, the Clarks reached out to Dr. Stanley Marks, a noted hematologist, at the University of Pittsburgh Medical Center. Marks, who was in New York, suggested a Monday appointment.
"I remember Ryan's exact words were, 'Doc, I don't think I can make it until Monday,'" Yonka said. "Ryan went in on a Friday morning, and by noon they were calling, saying, 'We want you in the hospital.'"
The Clarks credit Dr. Marks with saving Ryan's life. Marks, through the Steelers, declined ESPN's request for an interview.
Clark's playing weight is 205, but when he entered the hospital he had lost 40 pounds. Polamalu, with whom he is close, visited him there.
"That was probably the most crying I did in the hospital, was when he came to see me," Clark said. "It was so much more than football for me and him. I hadn't cried, not one time ... he started crying, too."
In two surgeries, in the span of a month, doctors removed his ruined spleen and gallbladder. When Ryan started joking with the nurses and picking on the doctors, Yonka knew he would recover. They cleared him to work out at the end of January and he traveled to Arizona to rebuild his dormant muscles.
"It was really awesome to see how he transformed when he started getting back in shape," Polamalu said. "This defense has been all about sacrifice, the way we throw our bodies around. Ryan's a prime example of that, obviously."
Said Yonka, "The NFL is not forever. I think it's a great thing that he accepts it as a blessing and is able to go out and play it to the fullest extent that he can, because it's only for a moment, and then, when it's done, it's over."
As fate would have it, the Steelers will play another game in the high-altitude of Denver in 2009. Asked whether he will play after all he has endured, Clark at first sounded cautious.
"It'll be a big decision, something we're definitely going to pray about," he said. "We're going to do our due diligence, finding what could happen."
He went on in this manner for some time with his wife nearby, listening intently. Still, there was something in his eyes that suggested the decision already had been made.
"You're going," his questioner said, not in the form of a question.
"No question," he said.
Greg Garber is a senior writer for ESPN.com.