Morgellon's disease is interesting, especially because of its fluctuating acceptance / lack of acceptance by the medical community.
When it was first named in the modern era (early 2000s) it got a lot of attention in the media and initially it was seem as a legitimate condition. Then it was dismissed (to the point of ridicule) by almost of all the wider medical community and seen as made-up (delusional parasitosis). Now it seems like more professionals are willing to accept it as a real condition, although the majority of medical professionals still don't believe it's real.