Their 2-0 victory over San Lorenzo in December represented Real's 22nd consecutive triumph in all competitions - a Spanish record.
A 4-2 friendly defeat at the hands of Milan followed, before La Liga and Copa del Rey reverses to Valencia and Atletico Madrid respectively at the start of 2015.
Real seemed to regain a measure of form with five straight league wins thereafter, but last weekend's 4-0 thrashing at Atletico drastically halted their momentum.
Some Real players attended Cristiano Ronaldo's 30th birthday party just hours after that heavy defeat, which drew the ire of supporters, and Ancelotti admits standards have perhaps not been as high as they were at the end of last year.
"We dipped in intensity and attitude since the Club World Cup," he said in a press conference on Friday. "That's all that has happened.
"I do not assess the privacy of players. The party does not affect the professionalism of the players.
"After the match versus Atletico, we were all frustrated. The critics we received were motivating and I saw that in training.
"I understand the frustration of the fans because it is the same as we have.
"[Club president] Florentino Perez spoke with us and showed he was worried. We'll try to find a solution for this problem.
"The dressing room is calm. The players give me confidence and I am sure that we will react."
Real sit top of the table, one point ahead of Barcelona, with Atletico three points further back in third.
With both title rivals not in action until Sunday, Ancelotti's men will have the chance to go four points clear when they host Deportivo La Coruna on Saturday.
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