BVB was dealt a devastating blow by Bayern, with goals from Mario Gotze on his return to the Signal Iduna Park, Arjen Robben and Thomas Muller giving the visitors a decisive 3-0 victory.
Jurgen Klopp's men have now lost three in a row in all competitions, and Blaszczykowski, acknowledging that the team is not in the best of spirits, insisted that it needs to put its slump behind it, starting with the Champions League game against Napoli.
"It's just a terrible situation at the moment," the Poland captain told Ruhr Nachrichten after the game. "We need to analyze it quickly, so that we can then look forward. On Tuesday against Napoli, we have to win. Before then we need to clear our heads. We must get back on track quickly."
Dortmund spurned a number of chances before Gotze's 66th-minute opener and, despite falling seven points behind Bayern, Blaszczykowski insisted that the home side played well.
"After losing 3-0, then the mood is obviously not good," the 27-year-old midfielder continued. "Up to going behind, we played well and also had opportunities. But we could not take them. We then we offered them too much space, which Bayern exploited with their quality.
"I don't think we did badly. Bayern rarely play as many long balls as they did but of course there is also the quality that allowed them to get away from our attempts to press."
Dortmund sits third in the Bundesliga with 28 points from 13 games, three behind Bayer Leverkusen in second.