Having this conversation with someone outside of 'family' who does not get to have a say if such a situation arose (God forbid) is extremely weird. If my boyfriend asked me this I'd definitely freak out. This conversation is only appropriate for parent-child, sibling or spousal relationships (or for people in long-term, committed partnerships). Perhaps your girlfriend wanted to imagine herself in a position where she would have the ultimate control over your life and death. Perhaps she imagined it as a sign of extreme intimacy between the two of you- sharing your darkest thoughts blah blah. Some people are a bit dramatic that way. If you are thinking of more sinister stuff...Well, only you can say if she showed any antisocial tendencies other than this.