If it is Astral projection you are attempting to achieve, it is a really unusual thing, as it is also considered an out of body experience. Because it was created by the new age group, and occults, it shouldn't be practiced. It is not something that your brain does naturally. Its normal to go into a state of dreaming, that shouldn't be confused with this.
You have to train your mind and learn, to get to the level of Astral projection, like a fortune teller looks into a crystal ball. When you attempt to control your own spirit, things can easily get dangerous. I wouldn't encourage it, especially with the warning "for those who can handle it, its really cool." We aren't made to practice such things, that's why its hard to handle it. You are becoming totally vulnerable to spirits that are feeding you the ability to achieve such things, and when you ask someone who teaches on the topic, they will tell you to pray and ask for protection from God, and the angels before you do it. That alone tells me that there is something involved with the practice that puts ones self in danger of being attacked spiritually, and would be like praying for help before you do something that God forbids, witchcraft, occults... Hebrews 10 26 If we deliberately keep on sinning after we have received the knowledge of the truth, no sacrifice for sins is left, 27 but only a fearful expectation of judgment and of raging fire that will consume the enemies of God.
Maremma is right, not all dreams that you feel you are in control of are Astral Projection. What separates them are, you know how to prepare yourself, and are attempting to achieve to get to the level where you can control them consciously, tricks to train yourself, sleeping on your back, and the other things you mentioned, those things make it sound like you prepare yourself to go into a state of mind where you are in control of them, when you are in a regular dreaming state, you do not need to prepare yourself, and they just happen. God can speak to you in your dream but you are in a state of mind that you are allowing Him to use you in a way that He sees fit, if its waking one up from a nightmare, or showing you something in a dream, if we are willfully, and attempting to be in total control, we can push God out of a dream all together.
What if God wants to show you something in your dream, but you are busy doing your own agenda with controlling it? Think about what you would be missing out on? God shows many things to people in their dreams. Sometimes, He will show you the way you need to go in life, or give you an answer to something you have been praying about, or show you something. God has shown me a lot of things through dreams. I wouldn't want to miss it doing my own thing.