Azrai, you almost made me choke on my food laughing at that one!
Besides what has already been noted, it could also be a living cat having an O.B.E. (out of body experience) when they are sleeping. Many animals do this. I've seen it a number of times with healthy pets of mine and of friends. They're sleeping, twitching up a storm and someone walks into the room saying they thought they saw the animal running, playing, or doing some other normal activity elsewhere moments ago and then vanish.