I lost my mother to cancer when I was fourteen. I will say that it never gets easier, but it does get easier to cope with. At the very least, I think you can rest safe in the knowledge that your anxieties, though over inflated, are rational and logical. It makes perfect sense to be scared of losing loves ones, especially after you have experienced it. So, I would say don't beat yourself up about the anxiety. For me personally, battling it or trying to ignore it usually makes it worse. I try to engage with the fear/anxiety, by understanding where it is coming from, and accepting its presence, whilst also knowing that it is an over exaggerated response. It is your brain trying to protect you, rather than you making a big deal out of nothing. Take a breather when the panic sets in, think about how relieved you always are when they do call back and everything is fine, and then go occupy yourself with something fun/exciting/interesting. And when the person that you are worried about does get back in touch, really revel in that relief. If this anxiety is something which is going to be part of your life, make it a blip, just the smallest of bad times - and make the good stuff/emotions so much better and stronger that they outshine the other stuff. The bottom line is that we all get scared/frustrated/fearful sometimes, but the trick is to make the good feelings so abundant and powerful that they make everything else look trivial in comparison.