Some of these cases are more bizarre than others. People can fake illness, and can be pretty good at fooling family, friends, and medical practitioners. But the story of Mary Toft was totally over the edge.
Toft captured the imagination of England when she "gave birth" to several rabbits and parts of other animals in the presence of numerous physicians and skeptics. The charade went on for months, perpetuated by daily newspapers, which were still a novelty. And back then, every newspaper resembled the Weekly World News, in which Bigfoot attacks are every bit as newsworthy as local politics.
It's true that physicians confirmed the story, although they were under political pressure to do so. Read this story and more at Cracked. Link
It's not exactly a hoax in the sense of these six stories, but the idea that the MMR vaccine could cause autism is one of the weirdest medical beliefs. One of the weirdest things about the whole story was the fact that most journalists didn't spot that the doctor responsible for this little "theory" happened to have a vested interest in discrediting the MMR vaccine until it was much too late. Journalists researching their stories? Yeah, they've heard of it.