i'm sure everyone has thoughts like that at some point (i know i do), because, if you think about it, dying is pretty easy to do, even by accident. but obsessing about that kind of thing is silly and pointless (unless you plan to use such depressing thoughts in a creative way). it's probably a subconscious thing - related to the books about holocausts, and maybe to do with uni. only last week i was discussing the possibility of the end of the world within my lifetime (cheerful, i know) and i'm almost certain that that was because i'd just read 'how i live now' by meg rosoff which, combined with the bombings recently, suddenly seemed very plausible, and reminded me about the general impermenance of things. anyway, i decided that there was no point dwelling unnecessarily on such things, as there is nothing i can do about terrorism. i think this is the attitude you need to adopt. it's true that you could die tomorrow (as could anybody) but worrying about it wouldn't change it, and all you'd do is waste perfectly good living time. try thinking about how lucky you are to be alive (and imagine how weird it would be if you weren't, because not only would you not be alive, but you'd never know that you had not been alive because you would never have been born and therefore you wouldn't actually exist). i know it's weird when you start thinking like that, and not particularly pleasant. if i were you, i'd find someone to talk to when you feel like discussing that kind of stuff, have a bit of a rant, and then find the cheeriest book or film that you can and read/watch it whilst pointedly blanking out any hyperchondriac-esque thoughts. it doesn't always work, but it can help.