A heightened sense of threat detection occurs in people who have generalized anxiety, which includes mostly everyone with a fear/anxiety disorder. In extreme cases nearly anything can be threatening and trigger defensive behavior.
LeDoux formally defines hypervigilance as the brain mechanism underlying inflated threat detection in anxiety disorders, linking it to norepinephrine/dopamine arousal and the misclassification of benign stimuli as dangerous.
, Anxious: Using the Brain to Understand and Treat Fear and Anxiety, 2015thesis