Truth is stranger than fiction when it comes to the extraordinary abilities of parasites to hijack other creatures minds... including our own.
Heads up. I'm starting with a spoiler. One of the most effectively scary movie moments I’ve ever seen is in the otherwise unmemorable 1979 When A Stranger Calls. A young babysitter keeps getting phone calls asking “have you checked the children?” Eventually she tires of the prank and contacts the police. They tell her to make sure all the doors are locked and if it happens again to keep the stranger on the line. The next time he rings she manages to get a few more words out of him, but he still hangs up quickly. The police call back. "We’ve traced the call. It’s coming from inside the house”.
For the rest of the story: http://www.bbc.com/future/story/20130328-the-mind-bending-enemy-within