People vary in their proneness to anxiety but it seems clear that a person who is vulnerable is also hypervigilant to their surroundings, especially if the situation is new, or relatively unfamiliar, or potentially intimidating.
The process of hypervigilance involves a rapid scan of the situation, which then narrows to a highly focused level of attention if a potential threat is spotted. The threat rapidly takes on a sharper and more defined quality and signals a change in behavior. The person may find a reason to escape or avoid the threat, or if this is not possible may remain in a state of high arousal and attentiveness in which coping behaviors (e.g. seeking something or someone to hold on to) may result.
Hypervigilance is characterized by increased physical and psychological arousal. Physically, the person may sweat, their heart rate increases, and breathing may become shallow and rapid. Emotional concerns can lead to a whole variety of behaviors that help make the person feel more secure. For example, carrying a weapon for fear of assault, or avoiding situations where people sit behind you, or being sensitive to sounds during the night and lying awake as a result.
Not surprisingly, hypervigilance is considered a common feature of various anxiety disorders, including post-traumatic stress disorder (PTSD). In some cases it can be extreme enough for the person to become almost entirely preoccupied with scanning their environment for threats. They may become agitated in crowded or noisy places and may adopt a variety of obsessive behavior patterns as ways of coping.
Pamela Cytrynbaum is a self-confessed hypervigilant. In her post for Psychology Today she vividly describes her feelings:
"It's around the corner. You will not be fooled or surprised. Everything is risky. Germs, driving, date rapists, identity thieves, breast lumps, pandemics, stranger danger, ebola, ecoli, left arm pain, child abductions, odd bloating sensations, racing heart rate, lower back pain, radon, Y2K, weird rashes, killer bees."
A few things do seem to help reduce the intensity of hypervigilism. One of these is exercise, which helps to burn adrenaline and release feel-good hormones at the same time. Another is relaxation, or forms of yoga or meditation. Breathing techniques are also useful and some simple techniques such as breathing in slowly and deeply, holding for four seconds then slowly breathing out as though expelling more air than was breathed in, may be helpful if anxiety builds as a result of perceived threats.