The Vikings locker room door swung open and the decibel level measured slightly above a whisper. The mood inside ranged from disbelief to downright shellshocked.

“I’m sitting here just thinking back [asking], what just transpired?” linebacker Chad Greenway said.

“Honestly, I have no answers,” defensive end Jared Allen said.

“I didn’t see our team coming in and playing as poorly as we did,” coach Leslie Frazier said.

Inexplicably, the Vikings treated their chance to remain relevant in 2013 with a collective yawn. Returning from their bye with a home game against a fellow 1-3 opponent, the Vikings looked so lethargic in a 35-10 loss to the Carolina Panthers on Sunday that the team’s medical staff should have checked everyone’s pulse.

A chaotic and somber week for the organization ended with a no-show performance that sent fans streaming to the exits at Mall of America Field midway through the third quarter and inspired those who stuck around to boo thirstily as the team bumbled and stumbled to the final horn.

The Vikings dropped to 1-4 for the second time in three seasons, and any optimism generated by their victory against Pittsburgh in London was buried beneath the rubble of Sunday’s dismantling.

How bad was it? Defensive tackle Letroy Guion actually was called for taunting after Carolina fullback Mike Tolbert broke four tackles gutting the Vikings defense for a 10-yard touchdown on a shovel pass.

“We didn’t handle situations very well,” Frazier said. “Poor job on my part getting our guys ready to play and play better.”

Frazier’s teams have been outscored 108-27 in three games following the bye. Predictably, Frazier and a number of his players said they needed to review the film to properly assess what caused their undoing.

Defensive end Brian Robison already had a pretty good idea immediately after the game.

“There’s nothing to figure out,” he said. “They came in here and they whipped our tail.”

Allen described his team’s performance as nauseating, which is probably how Vikings felt, too.

“I want to go home and throw up,” Allen said. “It’s embarrassing. This is one of the worst home losses I think I’ve ever had. If I’ve had worse, I don’t remember. The game was just blah. You look up and you’re getting throttled.”

Start with the offense, first. Matt Cassel threw two interceptions on wildly overthrown passes (including one on the opening drive) and could return to the bench next week to make room for newcomer Josh Freeman.

Frazier said his quarterback situation is undecided right now, and he left open the possibility that Freeman could start against the New York Giants next Monday night depending on his comfort level with the offense.

The Vikings weren’t able to run the ball, either. Adrian Peterson only had 10 carries, gaining 62 yards rushing as he played two days after his 2-year-old son died from injuries suffered in an assault that police say was committed by the boyfriend of the child’s mother.

“It felt good to get back out there, get into the swing of things,” Peterson said. “Offensively we weren’t able to get anything going, create any drives, be productive in the run or pass game.”

The defense was even worse. The Panthers had three touchdown drives that spanned at least 10 plays. Carolina held the ball nearly 13 minutes longer than the Vikings.

The Vikings couldn’t stop the run (131 yards allowed) or the pass (Cam Newton completed 20 of 26 passes for 242 yards and three touchdowns in posting a career-high 143.4 rating).

“When you can’t stop the run and you can’t stop the pass, what can you stop?” Allen asked.

The secondary doesn’t look capable of stopping anything at this point. Maligned cornerback Josh Robinson made another glaring mistake on the opening series of the second half. Robinson failed to drop deep enough in zone coverage, which allowed Newton to connect with Brandon LaFell on a 79-yard touchdown.

That gave the Panthers a 21-3 lead, and the Vikings played like zombies the rest of the game.

Afterward, someone asked Allen how the team can regroup after such an alarming performance.

“I hope people rebound by being angry,” he said. “I hope guys are ticked off. I hope their feelings are hurt. I’m a positive human being, and I believe in focusing on the positive. But I also believe there’s something to a little negative reinforcement.

“I hope this sticks in everybody’s gut a little bit, sticks in their craw and we can remember this feeling,” he said. “I hope that everybody is as ticked off as I am because this is embarrassing.”