"ki will leave your body and evil ghosts enter your body"
Joking aside this is known to happen and can. If you mess too much with your body and go against nature other things will too. It's nothing to do with having a stroke.
Are there any documented cases of this? I searched Pubmed and only found this http://www.ncbi.nlm.nih.gov/pubmed/12288176
(in this case ghosts = malaria)