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1. A failure to maintain a higher state
   - backsliding, lapse, lapsing, relapse, reversion, reverting

1. Deteriorate in health
   "he relapsed"
   - get worse
    
2. Go back to bad behaviour
   "Those who relapse are often minor criminals"
   - lapse, recidivate, regress, retrogress, fall back

Type of: change state, failure, regress, retrovert, return, revert, turn, turn back

Encyclopedia: Relapse