Some years ago, I became interested in lucid dreaming. I did a fair bit of reading on the subject, and one of the suggestions was that in order to condition yourself to question your reality, you should regularly pause and say to yourself, "Is this a dream? Am I dreaming now?" The idea is that you get so in the habit of doing this that you start doing it even when you're asleep, and it can trigger a lucid dream.
Doing that regularly did start to make me actually question my reality. Eventually, it became more and more spontaneous, i.e., I didn't have to ask or do a "reality check" any more to have the awareness of the "unreality" of my "reality". In time, this became a more or less permanent way of experiencing the world. I do sometimes step very deeply "into character", still, but that's no longer the default.
The amusing thing is that I'm no better at lucid dreaming now than I ever was. Now and then I still manage to become lucid, but for the most part, my dreams are entirely unconscious. So the technique did work, but not quite the way I thought it would...
