It's not uncommon to experience vibrations during sleep paralysis or lucid dreams. I usually get this strong zap in the back of my head, down by my neck, like there's an electric current running through it. It's also not uncommon to have audio/visual hallucinations during sleep paralysis, so if you were somewhat awake during it all, maybe that explains what you saw and felt?

The interesting thing is that people experienced with astral projection claim that these vibrations are exit points to leave the body. Apparently, when the astral body is either leaving or re-entering the physical body, there's this point where you're inside your body but still not perfectly aligned with it, and that's when you have the vibrations and usually can't move. It's called "projective catalepsy". So next time you feel the vibrations, you could try to leave your body and have an OBE... this is something I've been trying to do but with no success.

Hope that helps..