The situation was frightening, given that Kubiak had a transient ischemic attack -- or mini-stroke -- during a 2013 game while still the Houston Texans' head coach. However, the diagnosis of a complex migraine offered reassurance to himself and the Broncos, even though it will prevent him from coaching the Broncos for their Thursday game against the Chargers in San Diego.
Special teams coordinator Joe DeCamillis will take the reins on an interim basis, with Kubiak remaining back in Denver to rest and visit with doctors as he deals with the problem that set in Sunday.
"We're worried -- and happy for Kub's health at the same time," said DeCamillis, who was handed the reins in part because of his extensive role in game management, on which he works closely with Kubiak and the team's analytics director, Mitch Tanney.
"(With) the information that we received (Sunday) night about the different things that have happened, we felt very good about the fact that he was going to continue to be able to do what he does," Broncos general manager John Elway said. "That's the best thing. Sometimes these situations they're bad, but really good things come out of it."
Kubiak will spend the week resting and consulting with doctors. He was released from a Denver-area hospital Monday after spending the evening and morning receiving tests and his diagnosis -- and in between, getting some much-needed rest.
"He was very tired, but he got a great night sleep (Sunday) night," Elway said. "Probably as good of a night's sleep he's had in a long time."
But that wasn't enough for anyone to consider having Kubiak coach this week.
"We didn't give him a chance. That question was not asked," Elway said. "The doctors said, 'Hey, listen. This is Gary's week.'
"Gary is going to concentrate on Gary this week. Everybody else will concentrate on getting a win down in San Diego."
--The Falcons found the Broncos' weakness Sunday, and Atlanta exploited it repeatedly.
Using a similar tactic to one the New England Patriots tried to increasing effectiveness late in last January's AFC Championship Game, Atlanta spread running backs Devonta Freeman and Tevin Coleman out, lining them in the slot and out wide.
The strategy took the duo out of the backfield, but it also set up one-on-one battles with Broncos linebackers Brandon Marshall and Todd Davis, removing both from the box, where they could provide a delayed pass rush that often helped set up sacks.
"(Atlanta) spread us out, and we get that," Kubiak said. "The key part was that they had time to get those guys downfield. For backs to get downfield, it takes some time. You can't ask (Marshall) and Todd and those guys to hold up that long."
It worked brilliantly -- for 167 yards on seven receptions by the running backs, including gains of 31, 48 and 49 yards that were Atlanta's longest of the day.
"It wasn't their receivers. We shut them down," Broncos cornerback Chris Harris Jr. said. "That's how teams play us. That's how (Tom) Brady played us."
And it's something that the Broncos can expect to see again until they find a way to stop it.
--Trevor Siemian cited "a combination of a bunch of things" as to why he could not return in time to play against the Falcons, but according to one report, his absence -- and his potential absence Thursday -- is because of the severity of his left shoulder injury.
Fox Sports' Jay Glazer reported Sunday that Siemian's injury is a Grade 3 AC joint sprain, which could keep him sidelined for a second consecutive game since the injury occurred against the Tampa Bay Buccaneers on Oct. 2.
"I'll take it one day at a time and get right (Monday) and 'Greek' (trainer Steve Antonopulos) will have me doing some stuff, I'm sure," Siemian said after the Sunday game.
Added Kubiak: "We just didn't think that Trevor was ready. We watched him work Friday and talked to him on Saturday morning a little bit."
Siemian has a 99.6 passer rating for the season.
"He's very close," Kubiak said. "He did everything he could for us all week long, but we had to make a decision that at the end of the week, when it's time to go, he tried to get there. He worked extremely hard to get there. We just didn't think he was ready."
--Right tackle Donald Stephenson was held out for a third consecutive game because of a calf injury. Ty Sambrailo struggled in his place, allowing three sacks to Atlanta edge rusher Vic Beasley.
--Tight end Virgil Green sat out for a third consecutive game because of a calf injury he sustained late in the Broncos' win over Indianapolis in Week 2. He practiced last week and said Monday that he would play against the Chargers.
--Cornerback Kayvon Webster was held out of the Sunday game because of a hamstring injury he sustained at Tampa Bay on Oct. 2. Lorenzo Doss took his place.
REPORT CARD VS. FALCONS
PASSING OFFENSE: C-minus -- QB Paxton Lynch got a glimpse of what was to come when the Falcons stacked the box to show rush on his first third-down pass, then emptied the interior and had no one over the A-gaps on his second third-down play Sunday. The varied looks kept him off-balance, and RT Ty Sambrailo's inability to contain OLB Vic Beasley on the outside led to the disintegration of the pocket, leaving Lynch skittish. Lynch missed some open receivers, and he overthrew WR Emmanuel Sanders on what could have been a touchdown reception. A late flurry of completions against a Falcons defense laying back to take away the big play burnished Lynch's statistical line, but in the end, it was a day typical of a rookie quarterback.
RUSHING OFFENSE: D-plus -- Once again, the Broncos struggled to run the ball -- but this time it was against one of the league's worst rush defenses. Denver averaged just 3.5 yards per carry and failed to convert a pair of third-and-1 situations in the second quarter. The inability to get tough yardage on a consistent basis has been a problem throughout the season.
PASS DEFENSE: C -- LBs Brandon Marshall and Todd Davis struggled to cover Falcons RBs Devonta Freeman and Tevin Coleman, and that rendered moot the solid work of the Broncos' pass rush and the lockdown play of CBs Chris Harris Jr. and Aqib Talib on WRs Julio Jones and Mohamed Sanu. Falcons QB Matt Ryan wasn't as prolific as he was in previous weeks, but what he did was enough.
RUSH DEFENSE: C-minus -- Freeman and Coleman didn't just beat the Broncos downfield, they diced them on the ground, steadily chopping away at the Broncos' defense to combine for 119 yards on 29 carries and a fourth-and-goal touchdown run in the first quarter. Atlanta finished with just 3.8 yards per carry but moved the chains on 25 percent of their non-kneel-down handoffs.
SPECIAL TEAMS: C -- Brandon McManus was perfect on his placekicks, but poor decisions and execution on returns hamstrung the Broncos and left them losing the field-position battle. Cody Latimer elected to return three kickoffs from the Denver end zone, and he didn't get any farther upfield than the Denver 22, costing the Broncos 18 yards of field position. A failure to field a bouncing punt by Jordan Norwood also forced the Broncos to start at their 1-yard line in the third quarter; a play later, Lynch was intercepted.
COACHING: C -- Slow starts continue to be a problem for the Broncos, as who fell behind early at some point in four of their first five games -- including double-digit halftime deficits against the Panthers and Falcons. Against Atlanta, the deficit was too much to overcome.