The way that I can tell that it is different from a lucid dream is the feeling of the tingly vibrations, actually sitting up out of my physical body and I usually see it, and also the tremendous amount of control over the world you are in. I have always had lucid dreams, and have always been able to control them to a point. But the amount of control you have over your body, and the world around you when you astral project is non-comparable. It's an experience like no other-- when it happens you will know without a question. To me, it doesn't feel like I am dreaming--it's a totally different feeling.