Wenger's side have won nine of their last 11 matches to force themselves back into top-four contention.
"When you have so much possession and cannot finish a game off I am always a little concerned that the ghosts we had to fight one month ago will come back," said Wenger.
"We are not yet on a completely different planet and we still have to fight against it. Every win makes us stronger and I feel there is a desire from the team to do well.
"In the past when we have had a young side and it was going our way, that was a little bit of a weakness.
"Now we are a bit lighter in our display, a bit more spontaneous. That is linked with the confidence of course. One month ago we played here against Swansea and absolutely had to win, or else we would have had a complete disaster."