What does "hypervigilance" mean?

What causes it?
What behaviour does it cause?
any general info on this condition most welcome.Thank u.
Answers:
it is roughly equivalent to paranoia but not as pathological. it causes suspicion, higher levels of anxiety, possibly isolation.
Main Entry: hy·per·vig·i·lance
Pronunciation: -'vij-&-l&n(t)s
Function: noun
: the condition of maintaining an abnormal awareness of environmental stimuli <post-traumatic stress syndrome, marked by symptoms like frequent nightmares and repetitive anxiety dreams, insomnia, intrusive disturbing thoughts, hypervigilance and being easily startled —Daniel Goleman> —hy·per·vig·i·lant /-l&nt/ adjective

Merriam-Webster's Medical Dictionary, © 2002 Merriam-Webster, Inc.
It's usually used to describe the behavior of someone who has experienced trauma so severe that it leaves the person overly aware and reactionary to danger, whether than danger is real or imagined. The trauma typically relates to an abusive childhood, being surround by emotional or physical violence and/or having alcholic parents. It is a symptom of Post Traumatic Stress Disorder and one of the diagnostic criteria for an adult child of an alcoholic. Behaviors include sleep disorders, free floating anxiety, paranoia and emotional defensiveness.

We all experience it for awhile after a bad car wreck, but it is chronic in trauma survivors.
hyper = over

vigilance = The quality or character of being vigilant; watchfulness, alertness to danger etc.; close monitoring of a situation; caution

Politics (England):

This is used by people who disagree with you and do not like you to put you down because you see more than they do (but they have the power).

If this does not work, they will call you NOSEY, DISRUPTIVE, ANGRY YOUNG (WO)MAN, PEDANTIC (nearly as bad as being a Paedophile).

If you are not intimidated, the bullies will then extend their INSULTS to making up stories, false accusations, complaints to the authorities, all the usual tricks. Recognise your enemy. If he says he is doing it for your own good, punch him hard on the nose. (Make sure he is not vigilant enough first!)
It pretty much means being paranoid-but paranoid suggests "no reason". Hyper vigilance usually happens in crime victims such as rape, assaults, etc.. Victims usually believe the rapist if still out there can strike again and live in fear.

This hyper vigilance causes them to be extra cautious of people, places, and events, in order not to run into the person who committed the crime towards them. Sometimes it causes them to see the person again in another person, when it really isn't the perpetrator. The victim cannot usually go back to the place where the crime occurred.
Extremely insecure, paranoid, uncertain, superstitous, edgy. Normally caused by some sort of trauma.
Hypervigilance is an enhanced state of sensory sensitivity accompanied by an exaggerated intensity of behaviors whose purpose is to detect threats.

It is a symptom of a number of stress-related disorders