Hypervigilance is a symptom. Vigilance is the ability to stay focused upon a task and/or concept for an extended period of time. Think of it as the opposite of distractability. There are many (or most) things in life that require us to be vigilant. Some tasks such as child care, aspects of building construction and surgery require that we not lose our focus on the tasks in front of us.
However, hypervigilance is a symptom. It occurs when we are checking the environment for danger. We are hyperalert and are continually checking for both danger and safety. You are vigilant when you check the stove to make certain that the burners are off. You are hypervigilent when you repeat this and other behaviors continually and in an exhausting pattern, unable to stop, reassuring yourself that you are safe, that all is well and that you can now relax.
Hypervigilance is the opposite of both physical relaxation, emotional calmness and mental freedom. When hypervigilant you are a prisoner to remote and uneven unknown sources of danger.
When someone is injured on a motor vehicle accident, in a production facility, in a construction environment or in any setting in which vigilance could have minimized or avoided the accident, there is the increased probability that hypervigilance will emerge. The individual is unable to drive without excessive caution, work without checking and/or re-checking equipment and/or coworkers. Additionally, there can be a spread of effect in which this hypervigilance occurs not only in the setting where the injury occurred but also in only vaguely similar settings. And this generalization can increase over time.
Hypervigilance is a natural response to violence in which you become physically, mentally and emotionally prepared for additional threats to occur. An explosion triggers hypervigilence for subsequent explosions and an assault leaves one prepared for further or additional assault.
Thus, one of the symptoms of acute traumatic stress and posttraumatic stress is hypervigilence.
In combat, this “symptom” is part of survival; to relax would increase risk.
In summary, vigilance is a necessary tool to have available when performing any serious or detailed task. Hypervigilance is a symptom driven by fear.
You expect your surgeon to count all instruments at the end of surgery. You do not want him/her deciding to re-check the contents of your body.