What you are describing is living above "red". It doesn't matter where you are, what you are doing or who you are with you are constantly looking at peoples hands, faces, posture, and constantly assessing threats. Many people in law enforcement and military have the same experience as you.
The way I have heard it explained is as such:
green = this is where you feel most safe, this would be when you are home in bed, or when you are back in your old childhood room at your parents house.
orange = You are slightly alert, this can be your condition while driving, or walking on the street. You are aware of your surroundings, but you feel comfortable and at ease.
red = You are highly alert, you are scanning every single person, you are scanning all situations, you are watching for unexpected movement, you are watching facial expressions and body language, you are looking for exits, you know what locations would be safe and what locations wouldn't be safe. Some people have said they experienced a sort of tunnel vision in that you don't nothing anything but potential threats.
People that spend a long time in the red zone can have significant issues with PTSD, it can put you on edge, make it difficult to function in society. The reason why law enforcement feels like such an outsider compared to the general citizen is partly due to constantly being in the red. When they are around other police officers they can let their guard drop a little and feel less stressed.
I hope you soon start feeling like you don't have to do what you are doing. I've heard from friends that were in the military that for them it went away after a year or two of being out, but it has been difficult for them, you forever see all situations and people in a completely different light. Best of luck to you.
Note: I personally spend a lot of time in orange and red modes, part of this may be my life long martial arts training as well as having had attempted muggings. Even while at home I never leave orange, I have a hard time finding a place where I feel completely at ease/in the green.
I feel for the soldier you're replying to because he is at odds with society in this regard. However, he's not at odds with reality because bad shit really does happen and I admire his not being so quick to label it some kind of illness.
With hypervigilance you are identifying threats that do not likely exist given the current context of the situation. Classic post-war examples are where someone needs to check their corners before exiting an aisle of a grocery store or fears slowing down at an intersection because it leaves them vulnerable, even though they are in their hometown. It can interfere greatly with someone's quality of life.
[0] http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001923/ [1] http://www.ptsd.va.gov/public/pages/ptsd-suicide.asp
There are a couple of other things that need to go wrong until the diagnosis of PTSD is applicable. Sadly, this is not exactly made easier by the fact that people tend to have vastly different reactions and symptoms.
I think for me personally it is a highly anticipatory, self-protective mode. I am constantly assessing and "war gaming" where scenarios/situations might veer. This includes my daily commute, shopping trips and unfortunately romantic relationships.
There was something about the idea that I might have died in a grey train full of grey commuters, having not truly lived, that I could not stand.
It's just a bunch of hype.
Israel is a very safe place on the whole. You are far more likely to die here as a result of the horrifically bad drivers than of any other cause. Day-to-day, it is not "walking around on alert" as various (ex?)military members have related above.
What exists is a higher level of awareness, certainly for those who have ever been in close proximity to some… event—but also for society at large. I don't know what it's like in the UK, but I don't think there are bored underpaid security guards at the entrance to every mall with handheld metal detectors and an "open your bag, sir." this kind of casually intrusive security is simply unknown in the US outside of airports, at least until the DHS collectively lose their shit over a plot to bomb a mall using chewing gum, bleach, and a tweezers.
So yes, there is hype, particularly if your information is gleaned secondhand from the media; they only show pictures of things here when they're on fire. That doesn't conflict with my (personal, biased) experience that society here has a deeply-ingrained sense of "be on the lookout." I certainly felt it in Tel Aviv during the wave of bombings around 2000/2001 and intifada II, and I saw firsthand how America tried to come to grips with this unfamiliar sensation in New York during 9/11.
I wouldn't call it "a bunch of hype," but I agree that most of us don't live in fear. I object to the word "hype", as those that have experienced terror attacks don't forget them. The fear isn't exaggerated, but the frequency is.
...but how? Did you never spend significant time in Jerusalem (before they finished the separation wall)? I only spent a total of a few months in Jerusalem and saw one suicide bombing and was a few blocks from a shooting. Have you never been to the west bank? One of the two times I went to Hebron I saw soldiers shooting at...who knows? But they were shooting. If you live near the northern border or near Gaza you must have been exposed to rocket attacks at some point. The only way I can imagine you don't encounter violence over 25 years is if you live in a safe area and don't venture out much. Still, you must have friends or family who are exposed to violence. I find it incredible that you think it's just 'hype'.
I almost went to Thailand just before their little redshirt coup thing on vacation from Iraq, too. Fortunately I couldn't get a flight, so I watched it on TV instead a few days later.
It seems cliche, but there is a fundamental truth to the fact that most westerners are simply unaware of what the "I fear for my bodily integrity" sensation is and does to your life. OP's newly-discovered appreciation of how crowded buses present a potential security threat is a great example. It isn't that you suddenly see your life in a whole new light, it's that you regard various mundane things with a new, orthogonal parameter: is this situation more likely to result in harm to me?
Like all things, eventually you become inured and looking at a situation from a security perspective becomes a routine thought passing through your head along with "shit, I forgot to pay the gas bill." Without getting into Israel/Palestine, this is a slice of what living in Israeli society is roughly like.