Arsene Wenger's men lost 3-0 to the Toffees at Goodison Park in a crucial fixture that saw the hosts move ahead of their rivals in the race for a top-four spot.
|4/1||Olivier Giroud is 4/1 with Bet365 to score the first goal in an Arsenal win against West Ham|
"Against Everton, it's true that I wasn't on my game," he told L'Equipe. "That can happen in a season. I thought about it, assessed myself and now I'm back to work."
Arsenal are now two points behind Everton with just five games left to play and face West Ham at the Emirates Stadium on Tuesday, having already beaten the Hammers 3-1 this season back in December.
Giroud failed to find the net at Upton Park but believes that his side must produce an flawless end of the season if they are to claim a top-four spot and the FA Cup.
"There are six finals ahead of us, five matches in the league and the FA Cup final," he added.
"If we play without errors in the league, we'll qualify for the Champions League."