There were two “Learning to fly” threads in the Quest for Lucidity subforum. For instance this one:
Learning to fly in LD’s
There are two sorts of dream fading. What is actually called “dream fading” IMO, that is, you’re still lucid but visuals disappear quickly. Then you have to spin or rub your hands to make visuals reappear. Now if you spin, beware the FA! 
Do systematically a RC after this.
Or you can lose lucidity. It’s like what you describe, it happens gradually, you start to believe more and more that the dream is reality. This makes consciousness and vividness disappear until you’ll be in a ND. In order to avoid this, you have to stare at your hands or perform a RC from time to time, as I said above. This gives a boost to lucidity.