Just read this article on the good old BBC news site.
Western doctors are apparently stumped by outbreaks of "Grisi Siknis" or Crazy Sickness affecting teenagers in Nicaragua.
They clearly haven't read the bible much.
When people claim to have been possessed, you'll naturally want to find a more logical explanation that doesn't involve nasty spirits and such. However, when medical experts study it for years and come up short you've got to start wondering.