Today I learned that a sudden jerk that you sometimes experience when you are just about to fall asleep due to a sense of free-fall or weightlessness iscalled a hypnic jerk.  If, while sleeping, I roll over to the edge of the bed, I feel free-fall & jerk up from sleep if I am about to topple down.But in case I am comfortably lying down in the middle of the bed with no chance of toppling down, how do I feelweightlessness or free-fall when I am just about to fall asleep and jerk up, i.e. hypnic jerk?And not just on the bed; this is also experienced if you are sleeping on the ground where u cannot possibly physically fall.  A bit more research in Falling sensation  tells me its the ears & the eyes that sense the free-fall.  Sensation of falling can be induced when the eyes detect rapid  apparent motion with respect to the environment.  How is this accounted for during sleep. Or is it something entirely different?
How does the body experience free-fall during a hypnic jerk
neurobiology;perception;sleep;motor