The Ripper virus that Katherine injected Elena with started to take hold in The Vampire Diaries Season 5 Episode 16.
The difference between Elena and Damon is that Elena's virus was laced with werewolf venom. Not only did she want to feed off her friends, but the hallucinations kicked in quickly as her body began to deteriorate. Luckily Stefan and Bonnie thought to have new witch Liv do a boundary spell that would quarantine Elena to the dorms.
Elena's hallucinations led her to believe she killed Aaron Whitmore. Damon feared that Elena would hurt herself so he broke out of the Salvatore basement.
Stefan, Caroline, and Enzo worked with the travelers to get the antidote to the virus. However they want something in return that involves killing Stefan's doppelganger.
Meanwhile, Liv had everyone fooled that she's a newbie witch - but she and her brother Luke know way more than they let on.
Watch The Vampire Diaries online to find out what happened next!