The harsh reality continued to nag at him when he returned to Bank of America Stadium Monday morning, but he began to feel better when he watched game film from the beginning.
If only he could have hit the stop button before the final few plays.
"I was lying around thinking about it most of the night, and then coming in and seeing it, it doesn't change, obviously. What does change though is my opinion on what really happened in terms of what we did during the game," Rivera said.
"There were a lot of good things, a lot of things we're going to build off and use as we go forward. The bad part is that we had a very good football team against the ropes, and we didn't finish them off."
The Panthers played winning football for 59 minutes in a building where few visitors win, only to be stunned by an unlikely finish. Taking possession at their own 1-yard line with 59 seconds left, the Falcons drove 76 yards without the benefit of a timeout to set up Matt Bryant's 40-yard field goal for a 30-28 victory.
"Any loss is a tough loss, but when you have it won, it's even tougher," defensive end
Before the last-second punch to the gut, though, the Panthers went toe-to-toe with one of the NFL's three remaining undefeated teams, playing like a team capable of making significant inroads over the final 12 games of the regular season.
Offensively, the Panthers excelled in nearly every aspect of the game.
The running game piled up 199 yards, and the Panthers converted all three red-zone opportunities into touchdowns.
"The play of our offensive line, for the most part, was a huge plus," Rivera said. "(As was) the way DeAngelo (Williams) ran the ball. The play of our tight end. And our quarterback did some really good things.
"There are a lot of pluses, a lot of positives we can work off of and use to our advantage as we go forward."
Some of the same applies to the defense. The Panthers tied a franchise record with seven sacks, including a team-record 3.5 from defensive end
"The defensive line, their play – just look at what they did," Rivera said. "Charles Johnson did what I said he had been doing all year, and now he has the numbers to prove it. People were questioning what his impact was for us because he didn't have numbers, but now he's got three-and-a-half.
"The play of our defensive tackles – the Edwardses (Ron and Dwan) - was tremendous and really helped Charles out. Frank Alexander played really well, showed us his abilities."
The defense allowed just one score on Atlanta's four red-zone possessions and held on eight-of-13 third downs. And, in emphatic fashion, it ended its streak of allowing a touchdown on the opponent's first drive of the game.
In the end, though, it was all about the opponent's last drive, about the final minute that Rivera had to relive whether he wanted to or not.
"If we make a play, it's a different game, but now we're talking about ifs and buts," Rivera said. "The truth of the matter is we've got to be good enough to make those plays and continue to grow and get better.
"We are a young football team, but at some point you've got to get past that, because at some point you run out of time. We don't want to run out of time."