Manager Arsene Wenger said after back-to-back 3-0 defeats to Manchester City, including the League Cup final, that his players’ confidence was low and Chris Hughton’s team took full advantage on Sunday.
Lewis Dunk and Glenn Murray capitalised on poor defending to put the hosts two goals ahead, with Pierre-Emerick Aubameyang scoring a first-half consolation in a 2-1 loss.
Significant numbers of Arsenal’s travelling support were calling for Wenger’s head as they went two goals down but Koscielny called for a united front.
“We need to stay together, to fight together,” he said. “It is a big period for us. We know it is difficult but you need to put your head down and work every day.
“We need to win to have more freedom on the pitch and we need to stay together because it is a bad period but all the players, staff and fans need to know that we are all together. It is important to have everyone behind us.”
Arsenal have won just three away league games all season and have now lost eight of their past 13 games in all competitions.
Their miserable run has left them 13 points adrift of Tottenham in fourth place and Koscielny conceded it would be difficult to overturn such a deficit.
“It will be very hard to finish in the top four,” said the Frenchman.
“We have (had) a bad period and did not have the results we wanted. We lost our confidence a little bit and on the pitch we didn’t have the confidence we needed to push ourselves more and to play well with the ball.”