I have to say, I don't recall ever experiencing this phenomenon--while I was awake. I have dreamed, a couple of times, that what should look familiar has changed completely. Maybe it's to do with the way we see things? I seem to see--be aware of, that is--more than the other members of my family. Even when I'm driving, I'm the one who most often points out such things as "One of those cows is a deer". I haven't ever tried to train myself to be particularly alert; is this just yet another variable in what makes us all different from one another?