Swansea City scored twice in three second-half minutes to record a 2-1 win at the Liberty Stadium on Sunday, with Arsenal having suffered an even greater capitulation in midweek.
Arsene Wenger's side led 3-0 against Anderlecht in the UEFA Champions League on Tuesday with an hour played, but contrived to snatch a draw from the jaws of victory.
Szczesny bemoaned a lack of focus in both matches and called for immediate action in the forthcoming games.
"For the majority of the game [against Swansea] we looked solid at the back and we looked dangerous," he told the club's official website. "We had a poor five-minute spell and at this level it costs you.
"It's something that we need to focus on because it's been two games where short spells lacking discipline and focus have cost us.
"You can't just hope that the next one will be different and we'll get a bit of luck - we need to focus for 90 minutes and do our jobs properly offensively and defensively. Then things will change."
Sunday's defeat leaves Arsenal sixth in the Premier League table and already 12 points adrift of early leaders Chelsea.
