How could anyone eat at a time like this?

She is too amped up, wound tight as the tape around Peyton Manning’s aging ankles, pacing, screaming at the television. She rejoices at each first down with an exuberance once reserved for touchdowns — because, face it, the Denver Broncos’ offensive expectations have had to be dialed back this season.

As the game grinds toward a tense resolution, like so many in a schedule fraught with drama, she resists the urge to engage fellow fans on social media because, frankly, people are too full of snark and surrender.

And then the Broncos win. Or, less often, they lose. But almost always — 13 times in 17 games this season — the stomach-churning difference comes down to a single possession.

Then Tiffany Catellier, a fourth-grade teacher in Casper, Wyo., launches herself into a stress-reducing workout, a run around the block, anything to hasten the sleep she knows will be elusive for hours.

In such an emotionally taxing season, this is the normal state of affairs for fans like Catellier and others in a Bronco Country defined more by loyalty than geography. Sunday’s AFC championship game against arch-rival New England figures to be no different.

This season introduced a different brand of anxiety perpetrated by a team constructed with the bricks and mortar of a dominant defense shoring up an offense far removed from quarterback Manning’s aerial extravaganza.

“I don’t know if that’s going to get us a championship, but it’s almost like they force their will on these teams — all these fourth-quarter comebacks,” Catellier says of the new-look Broncos. “It’s different, and it took some getting used to.”

It has been a shared learning curve.

While Manning and new coach Gary Kubiak tentatively explored a new, more balanced offensive scheme, fans became accustomed to the idea of defense winning games — or at least holding opponents in check sufficiently until the faltering steps of the offense finally gained traction.

This 13-4 team’s margin for error has been tantalizingly slim: The Broncos have gone 10-3 in games decided by a single possession — within 8 points. In NFL history, only the 1978 Houston Oilers had more close wins. Three of Denver’s victories came in overtime; only the 2011 Arizona Cardinals had more.

Contrast that with the previous three seasons of the Manning Era, when the Broncos produced 27 double-digit margins of victory, and for the vast majority of the time, fans breathed easy.

“You love a blowout, especially if your team’s on top,” says 38-year-old Tim King, a lifelong fan in Colorado Springs. “But for me, as long as we win, I don’t care if it’s a one-point game. A win is a win. But people with a heart condition shouldn’t be watching these Broncos.”

Game 2 of the regular season hinted dramatically at the late-game heroics to come when a struggling offense suddenly ignited to tie the Kansas City Chiefs. And then the defense won it as defensive back Bradley Roby returned a fumble 21 yards in the game’s waning minutes for a touchdown.

“In 2013, Manning was lightin’ it up,” says Michael Dopheide, a 43-year-old fan from Thornton, recalling the quarterback’s record-setting performance. “You felt confident that they’d score points. Now, the simple fact is that when our defense is on the field, we have faith, we believe. But it’s stressful regardless.”

Of course, the return engagement against Kansas City, at home in November, marked a low point as Manning threw four interceptions and gave way to backup Brock Osweiler.

Catellier had driven down from Casper to attend with a friend and recalls the 29-13 beatdown as “the worst game I’ve ever seen.” On the 4½-hour trek home, she actually had trouble, for once, staying awake, so profound was the disappointment.

Osweiler started the next seven games as Manning healed from injury, interrupting the story line fans had anticipated since his arrival: A Super Bowl victory to cap a Hall of Fame career.

John Elway redux.

Suddenly, the Broncos appeared to be a team in full-fledged transition — while still chasing an elusive prize. As the starter, Osweiler went 5-2 including the final regular season game, when Manning returned to rally the Broncos to another close win over the San Diego Chargers.

That performance revived the old narrative, and once again cranked up anxiety levels beyond those felt during regular-season wins and losses.

Fifty-three-year-old Kirk Davis, a blogger and longtime fan in Colorado Springs, describes an urgency to this season as many see the Manning window sliding shut.

“It’s been building, and you could see it in the records of the last couple years,” Davis says. “Is this gonna be the year? Is this gonna be the year? I thought 2012 and ’13 were the best chances, the better teams offensively. I was thinking one of those two should’ve won the Super Bowl.”

In the stadium’s South Stands, where Denver resident Lori Costanzo is a third-generation season ticket holder, Manning’s re-emergence brought a new spark, even as fans there grew to appreciate Osweiler’s in-season audition.

“You could feel energy back in the stands,” she recalls. “It was palpable. Now that he’s back in, it adds to the urgency of winning Sunday and hopefully in February.”

King voices another concern born of this season’s anxious moments. What about the future? What will this team be without Manning? And is Osweiler, soon to be a free agent, the answer?

“It’s like trying to fill Elway’s shoes,” he says. “No matter how well Brock does, it’ll never feel the same way. I think there’s a high anxiety level on whether Manning will retire, if all of a sudden we’ll become that (4-12) team that happened a long time ago.”

But the quarterback’s late-season absence, coupled with a consistently dominant defense, helped Costanzo learn to put her trust in something beyond Manning’s tactical genius.

In an odd way, all the anxiety — given the team’s success— has produced a different strain of confidence.

“Even last week, I was frustrated at times, but somehow knew they’d pull it out,” she says of the come-from-behind playoff win over the Pittsburgh Steelers. “I never worried they’d lose that game. I knew something would happen. It’s certainly been a mindset change, but I’m OK with it.”

That fan mindset, she figures, has gradually come to reflect the personality of this team — which, in a word, is tougher than last season, reflecting architect Elway’s desire for a team that, in contrast to last year’s playoff capitulation to Indianapolis, will not go quietly.

“This is more of a kicking and screaming team,” Costanzo says. “They understand who they are this year.”

And after a white-knuckle season, so do their fans.

Kevin Simpson: 303-954-1739, ksimpson@denverpost.com or @ksimpsondp