I wanted to post a review on it, but there's no thread about Laughing Fit. I decided to make one myself, however. You can view it on Youtube.
Part 1 Part 2 Part 3
Summary: Xana decides to pull an attack via NO2 to kill 'em warrirors by laughter. Only way to stop the laughter is by using water. Meanwhile, there's a Romeo/Juliet play going on at Kadic and Yumi's parents seem to have problems on their marriage.
My opinion: I feel like I wasted a part of my life by watching this episode again. Only interesting parts were the Ishiyamas having problems (the highlight of the show IMO), the Ulrich-Yumi moment in her bedroom, Odd feeling stoned and his Julia Roberts line. Lyoko scenes were meh and the only cool thing was Odd being able to crawl below the surface. The rest of the episode was pretty much "meh" IMO. Ulrich's a sh*tty theater actor, painful to watch. The excessive laughter is pretty retarded.
5/10.