Ranning away and fearing: IE BELGON basis

Back (travel backward) = Serb. beg, bežati (go back, running away,
flee); Indo-European basis BEL-GON); Γρ. φεύγω (perf.
πέφευγα = Serb. pobegao fled; povukao se stepped back), Lat.
fuga (flight, fleeing, escape); paveo (frightned) Lit. bū́gstu,
bū́gau, bū́gti intr. (frighten; cfr. Czech uprchnout, Serb. prhnuti
ran away; Alb. frikë fear, Ger. Furcht, Eng. fright); baugìnti
(frighten), baugùs (fearfully); Russ. испуганный
(ispuganiy) frightened пугать (pugatь frighten; Slav. *běgǫ
in Russ. běgu (Inf. běžátь), Little Russian. bihú (run), as
OCS. neologisms priběgnǫ, priběgnǫti etc. (to flee), also OCS.
běžǫ, bežati (to flee), etc;
Ir. búal water… Serb. bojati se (be afraid), bojiti (paint), bujati
(overflow; bujica torrent).

Obviously, running away and fearing are the most closely related
notions.