I agree, it could be night tremors...just like sleep walkers (like my daughter on rare occasions) careful not to disturb them abruptly. I was told things like this are temporary...usually it is just a stage of growth...or maybe your child has special gifts in the sixth sense arena. Is he seeing monsters? or is he seeing people?
AboutKidsHealth: Health A-Z: Night Terrors
(Night Terrors in Children - Identify, duration and prevention)
and
Coping with Night Terrors
(Coping with Night Terrors)
I always try to find the
"logical" reasons behind everything, including medical reasons (mental/psychological factors) before assuming that something "paranormal" is going on. I am also very spiritual that think that children do see things we don't because their so open, new and susceptible (third eye) to seeing spirits. Go the logical route and I really like the monster spray idea (in a spiritual way - you can add frankincense oil in the water - this is a purification/clearing method) and spray in the corners of the room.
I know how crazy I might sound

. I try to see the perspectives on both logical/scientific/factual and the idealist/spiritual/religious/non-conformance concepts and find a balance between what I know is a fact and staying open to other ideas. Good luck and my heart goes out to you in this ruff time.