Children of the Corn IV: The Gathering (movie, 1996)

Grace Rhodes, who is studying to be a doctor, returns to her hometown as a strange illness is afflicting the local children. The symptoms include a high fever and spasms, but even weirder is what happens the next day: All those with the illness claim they are somebody else -- then they begin murdering the grown-ups. After her sister undergoes the same sinister metamorphosis, Grace comes to believe there is some connection to an evil cult figure who may be returning from the grave.