According to AFP, Merkel on Mondaysaid: "Of course when you have been on such an emotional rollercoaster then a defeat is much more painful."
"We have got to ensure that we in future election campaigns get the necessary majorities together."
The German chancellor made the remarks after the Social Democrats together with the Greens won a single-seat majority in the northwestern state of Lower Saxony legislature on Sunday, ahead of a national election due in September.
The victory of the center-left opposition in the eight-million-population state has set alarm bells ringing for Merkel's center-right coalition of Christian Democrats and its coalition partner, the Free Democrats.
The website of news weekly Der Spiegel described the result as a "nightmare" for Merkel.
After Lower Saxony, only the southern state of Bavaria is expected to vote before the general election.
Merkel's ruling alliance has lost a number of state elections in recent months.