Don't forget, because of 24/7 rolling news and social media, everything is magnified to a point where it feels so much bigger than it really is, so it's not surprising it's really preying on your mind.
I don't know how much explanations etc help you balance your emotional with your rational responses, but if they do, this is actually one of the safest times in history, in terms of violence/war etc, and someone put a calculation on one of the other boards showing how, if an event the size of the Paris attacks were to take place every day for the next fifty years in Europe, you'd have something like a 5% chance of being involved: so 365 days of attacks with 80 odd death toll, for the next fifty years. Trust me - you wouldn't bet a horse at those odds :-)
If you find those sort of "logical" explanations don't help, then I recommend trying your best to minimise your interactions with news media and things like FB (I don't use it, but from what I've seen on others, there's often a load of blooming rubbish spouted that will only intensify people's anxieties). Also, do not compulsively read/watch the news - there's a lot of evidence that survivors going over trauma in the early days after an event actually increases the chance of someone developing PTSD (they were evaluating the effect of early intervention in traumatised individuals, and discovered that it's counter-productive), and this relates to you in terms of how the brain works: our brain copes appropriately with traumatic events by processing them in a certain way, and by reliving these events (through keep watching news/ISIS videos/whatever) you are actually preventing your brain from coming to terms appropriately with these atrocities, thus fuelling your own anxieties in the process. I know that when something happens, you want to be glued to the news and analysis, but it's not actually mentally healthy if you are more leaning towards an emotional than a rational approach.
Finally, long-term, you might find CBT very useful indeed: it's great for when anxieties come from suppositions that aren't actually based on evidence - so things like "my boss didn't say hello, it must be because he hates me, why does everyone hate me, oh no, I bet I lose my job" etc rather than, "ah, he's busy with the new contract - ugh I know what that's like" etc - where you are looking at the worst-case scenario all the time, even though it's terribly unlikely. It really helps with this kind of catastrophic thinking (or at least, it did for me) and especially in helping you react and respond to intrusive thoughts.