▁meaning . ▁The ▁use ▁of ▁the ▁term ▁was ▁first ▁attributed ▁to ▁Dan ish ▁phil os opher ▁S ø ren ▁K ier k ega ard ▁( 1 8 1 3 – 1 8 5 5 ). ▁In ▁The ▁Con cept ▁of ▁An x iety ▁( also ▁known ▁as ▁The ▁Con cept ▁of ▁D read , ▁depending ▁on ▁the ▁translation ), ▁K ier k ega ard ▁used ▁the ▁word ▁Ang est ▁( in ▁common ▁Dan ish , ▁ang st , ▁meaning ▁" d read " ▁or ▁" an x iety ") ▁to ▁describe ▁a ▁prof ound ▁and ▁deep - se ated ▁condition . ▁Where ▁non - human ▁animals ▁are ▁gu ided ▁sole ly ▁by ▁instinct , ▁said ▁K ier k ega ard , ▁human ▁be ings ▁enjoy ▁a ▁freedom ▁of ▁choice ▁that ▁we ▁find ▁both ▁appe aling ▁and ▁ter r ifying . ▁It ▁is ▁the ▁anx iety ▁of ▁understanding ▁of ▁being ▁free ▁when ▁considering ▁undefined ▁possibilities ▁of ▁one ' s ▁life ▁and ▁one ' s ▁power ▁of ▁choice ▁over ▁them . ▁K ier k ega ard ' s ▁concept ▁of ▁ang st ▁re app eared ▁in ▁the ▁works ▁of ▁exist ential ist ▁philosoph ers ▁who ▁followed , ▁such ▁as ▁Friedrich ▁N iet z sche , ▁Jean - Paul ▁S art re , ▁and ▁Martin ▁He ide g ger , ▁each ▁of ▁whom ▁developed ▁the ▁idea ▁further ▁in ▁individual ▁ways . ▁While ▁K ier k ega ard ' s ▁ang st ▁referred ▁mainly ▁to ▁ambigu ous ▁feelings ▁about ▁moral ▁freedom ▁within ▁a ▁religious ▁personal ▁belief ▁system