mid-13c., wersnen "to make worse," also "to grow worse," from worse (adj.) + -en (1). The reflexive sense of "to get worse, become worse off" was elevated into literary use c. 1800-30, where formerly worse (v.) had served. Related: Worsened; worsening.

early 15c., "sudden attack, convulsion; periodic worsening of a disease," from Old French paroxysme, paroxime (13c.) and directly from Medieval Latin paroxysmus "irritation, fit of a disease," from Greek paroxysmos "irritation, exasperation," from paroxynein "to irritate, goad, provoke," from para- "beyond" (see para- (1)) + oxynein "sharpen, goad," from oxys "sharp, pointed" (from PIE root *ak- "be sharp, rise (out) to a point, pierce" ). Non-medical sense of "any sudden and violent action; convulsion, fit" is by c. 1600. Related: Paroxysmal.