Just throwing in my two cents here - the sensations you describe about feeling a heavy weight on you are very common physical sensations you would experience while going into sleep paralysis. It's just that you are conscious of them because your mind is awake. It's like your body is going to sleep because it thinks your mind is asleep too, but it's not - You can kind of trick yourself into experiencing sleep paralysis this way, and use it to astral travel. I've managed to do it a few times, and also experience the sensations of an "evil" presence walking around the bed, and breathing in my ear. I'm still not sure what this is - I often hear voices too when this happens. Work with it instead of fearing it, and you may have some fun!