From WordNet (r) 3.0 (2006):
relapse
n 1: a failure to maintain a higher state [syn: backsliding,
lapse, lapsing, relapse, relapsing, reversion,
reverting]
v 1: deteriorate in health; "he relapsed" [syn: get worse,
relapse] [ant: bounce back, get over, get well]
2: go back to bad behavior; "Those who recidivate are often
minor criminals" [syn: relapse, lapse, recidivate,
regress, retrogress, fall back]