Do you remember that night 20 scene from the movie Paranormal Activity where the girl gets dragged out of the bed by a demon.
Here I will try to explain how that special effect is probably done. They did not use a demon. It looks like a frame by frame animation that you can do yourself at home with the help of a friend using GIFPAL.
Using GIFPAL application, ask your friend to capture frames while you pose on the bed and on the floor as explained in that animated gif below. keep your leg in the air in some frames to make it look like that something is dragging you.
There are only 6 frames in example GIF but you can add more frames in your animation for more realistic animation.
If you don’t have a webcam, you can still take pictures using a camera or phone and use them with GIFPAL.