"You know how a bell vibrates? That's how my brain was going at that time," he said. "I think five minutes later, I came back to myself. I went back out there and played football."
What Cartwright never did when the hit happened? He never told Washington's medical staff his head ached.
He's not alone. Thirty of 160 NFL players surveyed by The Associated Press from Nov. 2-15 replied that they have hidden or played down the effects of a concussion.
The AP embarked on the most extensive series of interviews about concussions since the subject became a major issue this season, talking to five players on each of the 32 teams -- nearly 10 percent of the league -- seeking out a mix of positions and NFL experience to get a cross-section of players. While not a scientific sampling, many of the players answered with startling candor.
"You get back up, and things are spinning," Giants backup quarterback David Carr said, "but you don't tell anyone."
Now the NFL wants players to keep tabs on each other and tell their teams if they believe someone else has a head injury.
Told of the AP's findings, NFL spokesman Greg Aiello said in an e-mail that commissioner Roger Goodell spoke to NFL Players Association executive director DeMaurice Smith last week about "the importance of players reporting head injuries, no matter how minor they believe they might be. The commissioner said that process needs to include players observing and reporting to the team medical staff when a teammate shows symptoms of a concussion."
What emerged from the AP's interviews was a wide-ranging, unprecedented look at the way active players think about head injuries in a world where "getting dinged" and "seeing stars" -- and the potential long-term effects of concussions -- are deemed a frightening but perhaps inevitable consequence of their job.
Indeed it is. In recent weeks, high-profile players Brian Westbrook of the Philadelphia Eagles and Clinton Portis of the Redskins -- neither of whom was surveyed by the AP -- have been sidelined by concussions. Westbrook missed two games, then returned Sunday, only to leave in the second half with another concussion.
The NFL says its data shows an average of one reported concussion every other game -- about 120 to 130 concussions per regular season.
Of the 160 players interviewed by the AP, half said they've had at least one concussion playing football; 61 said they missed playing time because of the injury.
"We're obviously concerned by the data and by the information," NFLPA assistant executive director George Atallah said. "We believe that there's more relevant data and information that the league has on these issues that we'd like for them to share with us in confidence."
During the AP interviews, some players quickly replied they never had a concussion, then realized they weren't sure, such as Tampa Bay Buccaneers defensive tackle Chris Hovan, a 10-year veteran, who said: "I probably was just too young and too dumb to realize it."
Not that it's necessarily easy to miss -- or mask -- the symptoms.
Kansas City Chiefs wide receiver Bobby Wade told the AP he's never tried to hide a concussion but is sure it happens frequently in the NFL. "You see guys with their eyes rolling in the back of their heads," he said. "You see guys shaking their head trying to get it together. If there was a doctor evaluating them, I'm sure they would say, 'Your brain has taken trauma."
Some talked about not wanting to let down the team. Others mentioned the importance of avoiding any sign of weakness in a sport where "warrior" and "gladiator" are viewed as compliments of the highest order.
And then there is the fear of losing a roster spot in a league where the absence of guaranteed contracts makes some players willing to sacrifice their well-being somewhere down the road for a paycheck in the here-and-now.
Players spoke frankly about being afraid of getting the sorts of long-term problems seen in boxers; about hoping they will be able to remember their career highlights once they retire; about their wives' constant concern; about whether they'll be able to see their "kids grow up and have kids," as Houston Texans offensive lineman Eric Winston put it.
Others told of memory loss during and after games, of not being able to recall what particular play calls meant, or of "talking gibberish" to teammates on the field.
"The only thing I remember is coming out of the tunnel at the beginning of the game. And then -- a big gap," St. Louis Rams linebacker David Vobora said of a concussion he got this season. "But I played the whole game, until the last series, when I started asking guys questions, and they looked at me like I was crazy."
Asked whether they worry more about concussions than any other injury, 30 of the interviewed players said yes.
"I do often think about the damage I'm doing to my brain and my nervous system," Holliday said. "When does it catch up with you?"
Two-thirds of the players the AP interviewed said the NFL is significantly safer than it used to be with regard to the risk of concussions, thanks primarily to changes in rules and equipment, particularly helmets and mouthpieces.
But there are caveats.
"Players are bigger, faster, stronger," Baltimore's Birk said, echoing other athletes. "It's simple physics: Force equals mass times acceleration. It is a violent game, and there are inherent risks to the game itself. ... Collisions are becoming more intense."
About half of the surveyed players said they've been paying attention to recent news about NFL head injuries.
That includes a congressional hearing last month, when Rep. Linda Sanchez, D-Calif., said the NFL's resistance to accepting a link between multiple head injuries in NFL players and brain disorders such as dementia and Alzheimer's reminded her of tobacco companies denying a link between smoking and disease. At that hearing, Rep. John Conyers, D-Mich., asked the NFL and its players' union to turn over medical records for an independent review.
As attention to concussions has increased, so have the efforts by the NFL and the players' union to address the issue -- including working to update the joint letter and brochure they sent to all locker rooms in 2007 to educate players about head injuries.
Goodell told Congress he expects to announce "shortly" new funding for concussion research and that the NFL is trying to learn about "new practice techniques that will reduce the risk of head trauma outside of the games themselves."
Dr. Joseph Maroon, the Steelers' team doctor and member of an NFL committee on concussions, called the subject a "major priority" for the league. In a telephone interview, he cited an ongoing study in which helmet manufacturers' products are being tested and noted the NFL mandate of 2007 that every player undergo neurological testing in the preseason to establish a base line against which results can be compared in case of a concussion.
Dr. Thom Mayer, the NFLPA's medical director, said there are "good trends" in data he has seen, showing that "it appears that concussions are slightly down from where they have been" and that "it appears players are being held out, when they have a concussion, longer -- maybe twice as long." He did not give specific numbers.
In the AP interviews, players with more than a half-dozen seasons in the NFL said the league, its teams and the union do take the issue more seriously now than at the start of their careers.
Still, concerns abound.
One player voiced his feelings this way: "It worries me, because I have aspirations after the game to work. I'd like to be able to remember everything. I feel like in some ways, my short-term memory isn't as good as it was, already. I don't know if that's from getting older. I don't know. But you only get one brain, obviously."
The words of a grizzled veteran? No. That's 26-year-old Colin Allred, a Titans linebacker midway through his second NFL season.
Other players discussed the difficulties of determining when someone does, indeed, have a concussion and nervousness about accumulating multiple head injuries.
"The unfortunate thing in our business, more times than not, is that either guys don't know it or don't let somebody know it and continually play through those kinds of situations, where it's week after week, it's hit after hit, where they're not coming out of games and they never get healed," said Arizona Cardinals quarterback Kurt Warner, who's had two concussions in a 12-year NFL career. "And I think that's probably -- and I'm just guessing -- where the biggest effects are down the road, is guys that may not have a record that they had 10 concussions but probably had that or more so and just played right through it."
Several players said they refuse to allow themselves to contemplate the dangers of their sport because it would become impossible to perform well while devoting any shred of thought to concussions.
There also is some dark humor.
One player joked about eating through a straw at age 45, and Dallas Cowboys linebacker Keith Brooking said: "I tend to use it as an excuse with my wife when I forget something. She tells me to do something, and [I say], 'I've been hit in the head a lot, Baby. Sorry. I forgot."
Cowboys backup quarterback Jon Kitna spoke in more serious terms.
"I firmly believe you can be paralyzed on any play, and I believe there's going to come a time when somebody's going to die on the field from a hit on the field. Because the game is getting so fast, the big guys are getting bigger, and the little guys are getting littler, but the collisions are getting greater. That's the scariest thing for me," Kitna said. "What else are you going to do? Shut the game down?"