Uncontrollable fear (5)
I believe the answer is:
panic
'uncontrollable fear' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for panic that I've seen before include "Sudden overpowering anxiety" , "Flap" , "Take fright, lose the head" , "Overwhelming terror" , "Sudden overpowering fear" .)