relapse
n. countablen. a time when someone gets sick again after they seemed to be getting better. It is also used when someone starts a bad habit again after they had stopped.
n. a deterioration in health after a period of improvement; the recurrence of a disease or a return to addictive behaviour.
He was doing well, but he suffered a relapse last week.
The doctor warned that stopping the medication too early could lead to a sudden relapse of the infection.
While the initial recovery was promising, the patient experienced a minor relapse during the third month of treatment, necessitating a more aggressive therapeutic intervention.
From Latin relapsus, past participle of relabi (“to slide back, fall back”), from re- (“back”) + labi (“to slip, slide, fall”).
Often used with the verbs 'suffer', 'have', or 'experience'.