relapse

ot noun

1. The act or situation of relapsing. a drug relapse
2. An occasion when a person becomes ill again after a period of improvement
3. One who has relapsed, or fallen back into error; a backslider.

fe’l verb

1. To fall back again; to slide or turn back into a former state or practice. He has improved recently but keeps relapsing into states of utter confusion.
2. (of a disease) To recur; to worsen, be aggravated (after a period of improvement).
3. To slip or slide back physically; to turn back.