Synonyms for Relapse (same or very similar meaning)
WordNet sense 1 (deteriorate in health):
get worseWordNet sense 2 (go back to bad behavior):
lapse, regress, retrogress, recidivate, regress, fall backWordNet sense 3 (a failure to maintain a higher state):
reversion, backsliding, lapsing, relapsing, revertingFrom the ODE community, based on WordNetadd/edit