I have astral projected a hand full of times, but I have never felt this. The other day I was attempting to project. I had been practicing for about 45 minutes. I remember clicking out and then waking up again with my eyes closed. I then focused on mental ovement of my astral arms. Then I heard what sounded like a liquid metal, and then the earth started shaking! I mean it was a violent shake! And then everything. Stopped, I couldn't get out. Are those kind of vibrations normal? I was holding a piece of Moldavite crystal. Could this have changed the way I experience projection?
Perfectly normal. You were simply experiencing Sleep Paralysis... called many things. The Vibrational State being one. I don't think the crystal will have changed anything. I've never used a crystal and have experienced what you describe many many times. :)
http://www.astralpulse.com/forums/welcome_to_out_of_body_experiences/everything_you_could_ever_want_to_know_about_sleep_paralysis-t38734.0.html
Have a little gander at that.