Do you think that someone that sleepwalks has a whole conversation and does things that they cannot remember in the morning is possessed?
My cousins would do this, fairly regularly. The thing is, while they were able to function, at that time, as though awake, they are still partially asleep and only operating "in the now" - they likely are experiencing other sensations of the dream state.
One cousin came to my room when we lived in the same house, and stood in the doorway and talked to me about nonsense for twenty minutes, and asked me "where's the button"? And scrabbled along the wall with his hands looking for it. I told him "You're still asleep man, you need to go back to bed." He looked confused for a minute, smiled, and then said "I knoowwwww...." and turned and went back to bed and didn't remember a thing in the morning.
When we sleep, our bodies are supposed to be suppressed from any significant movement (so as to not injure ourselves when we try to run or fight in a dream), but when this suppression doesn't fully "take", we get somnambulism, in which people operate in a dream-state of manifested near unconscious operation, rather than conscious reason, which is why things that they say and do don't often make much sense.
Everything has a scientific and spiritual nature behind it. Since science really cannot give any specifics on this I tend to believe that the spirit side of the person is trying to be free of the body and you see this in their movement. It also explains why they cannot remember anything after.