How do I banish this mild anxiety I now have about my grandfather and parents health when they're all well?

You have seen a lot of traumatic events at a young age and you yourself had to undergo chemotherapy to win your fight against cancer. In a lot of ways that makes you more mature than your years and also stronger, because you had to fight your own battle against cancer but I still believe especially this horrific sight of seeing someone die in a terrible accident and to be an eye witness that is not something one can just brush aside and move on from that, you may well suffer from post traumatic stress syndrome and you should go to talk to a councellor. There are still people now, who only happened to pass the sight of 9/11 when the twin towers in York had collapsed and saw some terribly injured or dead people and they were not in the building but just from what they saw they still suffer from post traumatic stress disorder because they never sought help and they need it. Some people or soldiers who came just back from Afghanistan may need councelling from what they went through even if as soldiers they are trained for war and seeing death..it's still a different thing to hear about it that to witness maybe a good friend dying right next to one...therefore I believe you should just consider that you might suffer from posttraumatic stress disorder and one is aware of ones own and ones loved ones mortality. We will all die at some point and maybe it's a good thing to know when this will happen, because things can happen with the blink of an eye. Children die, accidents happen, totally unexpected and unforeseeable things can happen to anyone of us at any time but we have to learn to live our lives in the moment and not fear what tomorrow may happen. The best thing you can do is to show your granddad now how much you love him and spend quality time with him now.. then you will accept that one day he will pass on much easier and old people don't fear death as much as young people. Most old people are not afraid at all to die. They believe in the immortality of the human spirit and all they fear is to have to suffer from a really painful debilitating illness for a long time and they would prefer to have their loved ones around them when their last moment comes... but they are not afraid of dying unlike some younger people...xx