ORCHARD PARK, N.Y. -- One 10-minute conversation Monday with Karlos Williams captured the dilemma the NFL and its players face on the issues of concussions, player health and the future of the game as they try to balance the long-term risks of brain injury with the league's financial success.

Shortly before speaking to reporters in the locker room, the Buffalo Bills' rookie running back had completed his first practice in exactly a month. A concussion had not only robbed him of the previous four weeks of his first NFL season but also his ability to drive a car, watch television or help out around the house.

And yet, despite well-documented risks of lingering effects from concussions, Williams hasn't thought twice about continuing to play. He is, after all, a 22-year-old who will be paid more than $650,000 by season's end and nearly $2.5 million over his four-year rookie contract.

Williams made an immediate impact for the Bills: He was the most efficient running back in the NFL through the first three weeks of the season, averaging 7.75 yards on 24 carries. He made his first start on Oct. 4 against the New York Giants in place of an injured LeSean McCoy. On an otherwise routine play late in the third quarter, Giants defensive lineman Kerry Wynn broke through the line and dragged Williams through the backfield, trying to slam him down. Williams eventually succumbed, his helmet bouncing off the turf for a 7-yard loss.

He popped right back up and stayed in the game, but it's that play that Williams believes caused his concussion and began a slew of symptoms.

"I thought it was just my stomach acting up, throwing up," he recalled Monday. "Me just feeling a little nauseated. Headaches, pains toward the end of the game. I thought it was just me being tired, me being dehydrated.

"But definitely as I got home, I knew that something wasn't right. My balance was off. It wasn't dehydration. I was drinking Pedialyte and water at halftime, so it couldn't have been that."

A few hours later, a concerned Williams returned to the Bills' facility with his fiancée to meet with trainers, who began to put him through the NFL's concussion protocol. The feeling of a concussion wasn't new to Williams; he suffered one in a car accident before his senior season at Florida State and another against Florida that kept him out of the ACC Championship Game.

Williams' third career concussion, and his first in the NFL, would take its toll over the coming days and weeks.

"It was pretty bad," he said. "Having really bad headaches. Not being able to sleep. Not being able to eat. Kind of side effects I've had over the years from having concussions: just being very, very groggy. Wanting to be up. Wanting to watch things. [But your] eyes hurt real, real bad. Very sensitive to light. Things like that. You're always tired. You can't sleep. Your head's always kind of pounding, throbbing. Your head feels tight.

"Headaches. Headaches. Bad headaches. Almost a migraine. Your eyes sort of hurting, felt like a lot of pressure in your head. Nausea. Dizziness. Getting up very quickly -- say, you get up quickly in the middle of night to go to the bathroom -- getting up quick kind of shakes your head around."

Williams and his fiancée turned off the lights in their house and closed their blinds. Their television stayed off. Williams couldn't drive for a week and a half.

"Going to the gas station, going the convenience store, going to get something to eat was kind of difficult at first," he said. "Me having to pack up me, my daughter, my fiancée every time we leave the house to get something to eat was kind of difficult. But as time went on, I was able to drive myself to the stadium to check in. Only driving once a day to come and check in.

"Other than that, my fiancée was running a lot of errands for us to make sure things got done for us around the house. She kind of stepped up and took my role. Taking care of stuff around the house. Big thank you for her. But driving, I wasn't doing a lot of that."

Some of Williams' rookie teammates -- wide receiver Dezmin Lewis, offensive tackle Tyson Chandler and defensive end Cedric Reed -- came over to visit.

"Just really trying to get myself around people," Williams said. "Am I communicating properly? Can I respond normally to people? That was kind of difficult, and getting used to that was kind of hard."

Even though football had put him in that condition -- recovering in a dark room from a brain injury -- he wanted to keep the game close by. It was still his livelihood.

"My fiancée was always talking to me about football, always trying to keep football coordinated into my life in some way," he recalled. "Watching football on Sundays, it is kind of down not being able to play. But having the support there, you're able to watch football and have somebody to talk football with, keep you in the football loop and not feel like you're such an outsider."

The road back to the practice wasn't smooth. He gradually reintroduced light and sound into his life, whether it was watching football or his daughter's television shows. But as Williams attempted to start weightlifting again, he experienced more headaches.

"It's kind of hard," he said. "You have to start all over again."

Having to restart portions of the NFL's concussion protocol is one thing, but starting anew in his life -- without football -- is not an option the young father has considered.

"I've got a hard head. I've got a very, very hard head," he said Monday. "My family will tell you that. But no, it doesn't frighten me at all. Concussions are freak accidents. Nobody goes into a game trying to give somebody a concussion. Nobody goes into a game thinking they're going to get a concussion.

"It kind of just happens. Some are worse than others, some are not bad at all. Some terrible. I think it depends on the blow you take or the person that's actually taking the hit. Some people can make concussions worse by not doing things properly or by not taking the right steps to get better and better. I think that leads to people not continuing to play the game of football when you don't take care of yourself after receiving a concussion."

All indications are that the Bills and Williams have taken the proper steps in his recovery. He was back in uniform Monday and, although he hasn't been cleared for contact, he's closer to a return to playing -- whether it's Sunday against the Miami Dolphins or one of the Bills' other eight remaining games.

When he returns, Williams' latest experience with a concussion won't change how the 6-foot-1, 230-pound bruiser approaches the game that America loves, as much as the risk of brain injury might threaten his long-term health and the future of the game itself.

"[I'm] ready to play football," he said. "It's not going to change the way I run the football. It hasn't changed the way I run the football. I run the football with attitude, and I think that's what the coaches expect from me coming back."

Welcome to the NFL.