An indicator of overall anxiety endlessly alarming from the start (5)
I believe the answer is:
arrow
'an indicator' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for arrow that I've seen before include "production of Fletcher?" , "Move quickly" , "broadly distinguishing old convict" , "Cupid's projectile" , "Missile for bowman" .)