What are these called?

Usually every night when I try to go to sleep I'll get a really strong sensation that I am falling off of my bed, or that my arms or legs are moving without me controlling them. These sensations will only last a second, but they startle me, and sometimes it makes it hard to go to sleep in the dark...

Example:

I'll lay down, close my eyes, and relax. As I'm starting to fall asleep (you know, slight numbing, ringing sounds, voices, etc.) I'll often get a sensation as if I've gotten stuck between a dream and the waking life. For a second, I'll have an hallucination that my body will fly up into the ceiling really quickly and I'll fall back into my bed. These sensations always have that roller coaster drop feeling.

When these "1 second nightmares' as I've called them happen, I will know that it isn't really happening. I'll just relax for a minute and suddenly feel my body fling out of bed. It's freaky!

Does anybody else go through something similar?

Yes, they are known as "vibrations". When doing a WILD technique you go through this. Read up on WILDS, you will find you can go streight into a dream while keeping your mind awake. (if you didn't know already.)

sounds like you must slip into sp if you stay still and relax you might in into a dream probley not though if its when you are going to sleep.