Vertigo

From Code Lyoko Wiki

In the episode "Vertigo", William Dunbar challenges Ulrich Stern to a race up a rock climbing wall. After being prodded by William, Jim Morales, and Odd Della Robia, Ulrich reluctantly accepts, and halfway up the wall, Ulrich accidently falls onto the matt below. Yumi Ishiyama comes to the conclusion that Ulrich has vertigo, and Ulrich storms off to get over it.

Meanwhile, Jeremie Belpois gives Aelita the supposed "antivirus." This doesn't help any for Aelita begins to become trasparent/invisible and because XANA has possessed a few wolves in the forest, where Ulrich had went to go sulk.

Now,Aelita goes to deactivate a tower, but she can't get into the tower to deactivate it because the towers no longer recognize her. Just in time, Jeremie manages to turn off the antivirus and Aelita deactivates the tower. Jeremie activates a return in time, and Ulrich is once again challenged by William Dunbar. Ulrich says that he has vertigo just as William has arachniphobia. When William asked how he knew Ulrich turned to look at Elizabeth Delmas (Sissi) and she winks.