The Gunners suffered their worst ever start to a top-flight campaign, including an 8-2 mauling at Manchester United and a 4-3 defeat by Blackburn Rovers to leave them in the drop zone after five games.
But the north Londoners recovered and clawed their way back into contention for Champions League qualification, and currently occupy third spot ahead of their final game of the season at West Bromwich on Sunday.
Centre-half Koscielny admits the stuttering start to the campaign caused he and his team-mates to question everything – including Arsenal boss Arsène Wenger – before they finally found their feet.
“The beginning of the season was a catastrophe,” Koscielny told France Football. “We’d lost players who were key to our system. We recruited late, and it took a while for us to jell. We were ‘whopped’ at Old Trafford.
“Everybody thought we were dead and buried. But you don’t lose your football like that, like snapping your fingers. It can happen that a grain of sand falls in the machine, and the machine stalls; then you start to have doubts about your qualities, your club, your coach, everything.
“We had to put the house back in order. And everyone did their bit: the coach, the club, because we were in a critical situation.
“The squad wasn’t giving enough for the club, and was aware of it. We got back to work, we told each other the things that needed to be told; after which, one win, two wins, confidence comes back, and things follow from then on. The new players gelled in the squad, and here we are.”
Koscielny, 26, admits his side’s biggest regret was their failure to perform in the 4-0 defeat by AC Milan in the first leg of their Champions League last-16 tie at San Siro.
He continued: “We might not have dominated every single game, but, mentally, we had something extra. At Liverpool, for example, we always believed, and Robin [van Persie] gave us victory at the very end.
“The biggest regret is, perhaps, the first leg against Milan, when the game completely passed us by. Arsenal’s place is among the top four clubs in England. A club doesn’t ‘die’ like that, and the players realised it.
“There weren’t too many people to accompany us in this climb back [to our place], but we did it.”
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news