From Longman Business Dictionary
relapsere·lapse /rɪˈlæps/ verb [intransitiveI] to start to get worse again after things had seemed to improverelapse intoThe U.S., after a brief recovery mid-year, is relapsing into a second slump.
—relapse /rɪˈlæpsˈriːlæps/ noun [singular]Industrial output rose, lessening fears of a relapse.