re·lapse 
(rĭ-lăps)
(rĭ-lăps)intr.v. re·lapsed, re·laps·ing, re·laps·es
1. To return to a former state.
2.
a. To become sicker after partial recovery from an illness.
b. To recur. Used of an illness.
3. To slip back into bad ways; backslide.
n. (rēlăps, rĭ-lăps)
A return to a former state, especially after apparent improvement.
[Middle English relapsen, to forswear, from Latin relābī, relāps-, to fall back gradually : re-, re- + lābī, to slide.]
re·lapser n.