The defending premiers are yet to officially book their finals ticket after falling to 13-5-1, thanks to a humbling 66-point loss to the Suns on the Gold Coast on Saturday.
The 20.10 (130) to 9.10 (64) romp was the Suns' biggest derby win and gave them a club-best 12 wins this season as they seek a maiden finals foray.
Usually dominant in the midfield, the Lions were outgunned as ruckman Jarrod Witts provided good service to Matt Rowell, Noah Anderson and Alex Davies.
It was only the Suns' second win in the past 14 QClash contests.
Fagan estimated fans "wouldn't have seen a performance like that too often in the past six years".
"Our last eight games we've won six and lost two. We've been up for a fair while and tonight we were really poor in every facet of the game, to be honest," he said.
The Lions face table-topping Collingwood at the MCG on Saturday, then host Sydney, travel to face Fremantle and finish the regular season at the Gabba against Hawthorn.
"It is hard to stay up every week, there's no doubt about that," Fagan said.
"That's part and parcel of the challenge.
"How you reflect on it really is how you react next week and how you play next week.
"We've got a pretty hard game ... I'm confident our group will respond, they normally do."
Utility Conor McKenna, who had won his spot back in the side this week, will have scans after being substituted at halftime with a hamstring injury.
12°C