Nouns

(n)backsliding, lapse, lapsing, relapse, relapsing, reversion, revertinga failure to maintain a higher state

Verbs

(v)get worse, relapsedeteriorate in health“he relapsed”
(v)relapse, lapse, recidivate, regress, retrogress, fall backgo back to bad behavior“Those who recidivate are often minor criminals”