The Terriers will head to Manchester United on Boxing Day sitting four points adrift of safety after losing at home to fellow strugglers Southampton.
Victory would have taken Town out of the bottom three for Christmas, but an error-ridden display meant the Saints were able to coast to a 3-1 victory.
“The first half was the worst in a long period for us,” said Wagner, who hopes to have Jonathan Hogg back at Old Trafford after the midfielder had to sit out Saturday’s game with a knee problem.
“It looked like recent results had affected us. We looked nervous, not calm. We looked rushed and we were not brave enough on the ball. The second half was better, especially offensively. But we can only get points if we perform at our highest level.”
Philip Billing’s second goal of the season shortly before the hour mark did briefly give Town hope.
But Huddersfield’s struggles in front of goal – they have scored just 11 times in 18 outings this term – meant Southampton were able to withstand that second-half rally to prevail.
Asked if he was targeting a striker in January, Wagner, who has been linked with Liverpool’s Dominic Solanke, replied: “It is obvious when you play 18 games and you have no striker who has scored a goal that this is nothing that we like to have.
“But what this means for January or for the window I cannot give a serious answer. We have to make sure we do everything to score, strikers or not.
“To be totally honest, I was surprised about the first half. This is why I was more frustrated. We are where everyone predicted us (to be in the league) so it makes no sense to be affected by it.”