Literally Falling Asleep

I decided to take a nap today because that is when i get closest to having an ld. As i was nodding off i tried that new ssild method and started letting my mind wonder and drift past random pictures and sounds. Then i focused on feelings and i got this falling sensation, like i was on a sudden-drop rollercoaster. i decided to focus on it, and it happened again, but er, and again, but er. I kept focusing but eventually fell asleep into a normal dream. What was this feeling i was experiencing and how can I use it to my LD-inducing advantage?