nocebo effectno‧ce‧bo ef‧fect /nɒˈsiːbəʊ ɪˌfekt $ nɑːˈsiːboʊ-/ noun [singular] 
when someone becomes ill because they expect something to make them ill, even though it has not actually done this
when someone becomes ill because they expect something to make them ill, even though it has not actually done this