The symptoms of hypervigilance include hyperarousal, constantly scanning your environment for danger, being easily startled by loud and suddden noises, being jumpy, extreme muscle tension, difficulty relaxing, always "juiced-up" or primed for action, difficulty sleeping, and irritability. Hypervigilance usually comes about with post traumatic stress disorder (PTSD), which develops after being exposed to a life-threatening trauma.
The following video explains how PTSD symptoms, such as hypervigilance, develops after exposure to a trauma:
