I think in those specific situations (sleeping, showering) your (an my) fear is heightened because we are vulnerable. If you are sleeping, it is very easy to be completely unaware that someone is doing something to you or about to do something to you until it is too late. In the shower you may be awake, but it is more difficult to hear, and you aren't exactly dressed and ready to run out of the house if you need to. It makes us feel powerless and helpless. Plus, even though it isn't likely that something will happen, it's absolutely possible.