Well, I guess the twitch that people do (including myself) right after falling asleep is perfectly normal according to some researchers.

This strange falling sensation and muscle twitch is known as a hypnagogic myoclonic twitch or “Hypnic jerk” If this has happened to you on more than one occasion, don’t worry, you are not alone. Close to 70 percent of all people experience this phenomenon just after nodding off, according to a recent study at the Mayo Clinic.

Most experts agree that this is a natural part of the sleeping process, much like slower breathing and a reduced heartbeat. The occurance is well known and has been well documented. However, experts are still not completely sure why the body does this.