Thank you once again, Eowyn, for all your time and effort to answer me.
I guess I have to become aware of mental projection. A quick look at Wiki learned that this can be done in a meditative state, and I saw something about the mental body as well.
I did leave my body twice several years ago. It was when I had decided to start 'classical' meditation. I woke up at 4 AM, did some meditation, and than went back to bed. And than... bang... I left my body with a great force like a projectile being fired(45 degrees up), stopped suddenly, and I hung in complete blackness. I realised what had happened and... bang back in the body. A few seconds later I got fired again, straight up (I guess about 50 cm), than the body turned itself upside down, and I went face forward back through my body and my bed and floor, untill I stopped again. Everything was black. I could hear my son opening his bedroom door, heard his footsteps in the hallway, and I myself hung somewhere in the neighbours appartment I guess. The noises were loud and anoying, like I was in a huge clockwork, and I heard the wheels turning, I heard thick chains making sound, scratching of stones... So I wanted back to my body.
I didn't like this experience at all. I never did this classical meditation again. and I was not really sure I would like to experience that firering force again, because it happened without my will. I prefer more subtle ways.
Some weeks ago I read your instruction about astral projection, and I talked about it with a close friend. She said to my surprise: I can do that too. I asked her why she had never said that before, but to her it is so normal, she doesn't even think about it as special. Every night she leaves her body consciously, doesn't go anywhere, she just hoovers about 50 cm above her body and than tells herself to fall asleep. I asked her if she can move around. She did as a little girl, but than her mother had told her that it was dangerous, and from that moment she never wandered around anymore, and stayed close to her physical body every night.
It took only little persuasion from my side (wicked me!!) to ask her to visit me next time. She did, could tell what happened in the house, could describe the interior of my bedroom. She also offered to help me leave my body... lol.
Well, she tried and she was convinced on forehand that she would be able to do that. But it didn't work out. She later told me she tried hard, pulling my astral hands untill she thought she had succeeded, but in fact not. Me, I did't see her, didn't notice her, but I did notice a presence that radiated a great feeling of safety. I joked inside of my head that if it was her, I wanted her to be my spirit guide for ever, such a safe feeling. (and afterwards she did tell me she was standing next to my right shoulder, just where I felt this cloud of safeness. And one moment I felt lifted completely, about 10 or 20 cm, but nothing more.
So she just recently started to explore the astral worlds, but she is not sure about all the things that happen to her. She knows she is out of her body. Her visits to me we can verify, but she can also switch to places she cannot verify, or even to a fantasyworld: her own novel. She can step into her own created 'reality' and talk with the characters she created herself. They live their own life, and when asked, give their (unpredicted) opinions.
I told her not to worry about this being astral projection or being fantasy, but to enjoy it fully. It must be a writers dream to visit your own created world just on command.