Is This Happening Associated With Ap? Options

When I use to be at my grandma's house all the time, I would go upstairs into her room, turn the TV on and relax on her bed. Most of the time I'll get this feeling that I'm falling. It's sorta hard for me to describe. But right before I hit the ground I wake up but with a jerk or I guess you could say a snap. This would only happen at my grandma's house too, maybe it happened once or twice at my house but it always seemed to happen in my grandma's house. I read somewhere that this was the astral body snapping back, I was wondering if this was true (IMG:style_emoticons/default/confused012.gif) Any suggestions on what this could be?

It's a hypnic jerk.