When Sunday dawned, the Lions held the NFC North lead. By Monday night, they were holding their heads.

And their own throats.

The Lions became the Lions. It’s like the Canucks becoming the Canucks. The Cubs in shoulder pads.

The Lions’ implosion is the feel-good story of the Bears season --- no worse than second behind Shea McClellin’s injuring Aaron Rodgers.

McClellin’s sack of Rodgers was a shocking spasm of quality play. The Lions, though, remain among the most predictable and enjoyable chokers Chicago could want.

They’re dirty and stupid, and now they’re in third place. The laugh-out-loud Lions were must-see TV. Again.

Calvin Johnson dropped passes. Matthew Stafford made horrible throws. The Lions were unprepared to win the biggest game of their season at home. Your work here is done, Jim Schwartz.

Baltimore kicker Justin Tucker booted a 61-yard field goal in the final minute to give the Ravens the lead Monday night. Stafford threw an interception on the next play to give the Ravens the win. So Lions.

Turnovers. Penalties. December gagging. Who would’ve guessed the Lions would devolve into that?

Besides everyone, I mean.

“You can’t trust the Detroit Lions because of games like this,’’ ESPN analyst Trent Dilfer said. “It was all there for them, and they threw up on themselves.’’

All of a sudden, the Bears control the NFC North. If they win out against the Eagles in Philadelphia and the Packers at home, they win the division and cop the third seed in the playoffs.

They probably would face a team with a better record in the wild-card game, but then, a wild-card game didn’t seem like a possibility after losses in Minnesota and St. Louis a couple weeks ago, especially after Marc Trestman ordered the field-goal try on second down in overtime against the Vikings.

Speaking of Trestman, and why not, speaking of Jay Cutler, too, they are the focal points of a surprising dream scenario.

Since Trestman left Cutler to stupidly hobble around in a loss to Detroit that cost the quarterback a month of games, the Lions have choked four of their last five. The Bears survived a dubious decision. Football karma is as much a fairytale as “Bear weather.’’

So now, the Bears will need a ton of points the rest of the way. There’s no chance the Bears defense holds LeSean McCoy to less than 800 yards Sunday night, and there’s little chance the Bears reinjure the returning Rodgers the following Sunday, a game that also probably will be flexed to a prime-time slot.

So the Bears will need points. The Bears will need Trestman to stay as hot as Cutler said he was in Cleveland on Sunday. They need the fourth-quarter Cutler, not the mess that threw up on himself the first 25 minutes, to steal a phrase.

It will be on Trestman and Cutler. They can’t go all Schwartz and Stafford now.