What are the exatly? is it the white and black swirlies you see when you close your eyes for a long time? or is it when your drifting off you start to to dream?

I think I had it before.. alot of people say its scary, (Now it may be scary for me)
but I think its the jerk thing right? I had one of these. I was watching a movie when I was 12 and I was drifting, and I seen me walking down the stars from band class. and it was like there was no gravity, then my feet went out from under me and i jerked. (I love this lol)

so this also happens to me when I WILD.. is this ok?