My wife and I and youngest son of five years old were living in an upstairs appartment.  Late one evening approximately 11:00 pm I was the only one up watching tv.  The lights were out but I could look approx. four-five feet to the right of the tv and see the hall and into my sons bedroom.  Let me set the scenario a little here.  If you go through that living room door and into the hall to the left is the kitchen that has a small night light that illuminates the hall slightly and in my sons bedroom there is also a small night light on the far wall that has very little illumination from it.  Well something caught my eyes coming out of his bedroom, all I could see was a black mass approx his height (i figured it was him and he being silohetted by his night light).  I said to him, "Hi bud, going to the bathroom?"  He did not say anything.  Well a couple of minutes went by and I got to thinking that maybe he was sick or something. I went into the hall and to the right to where the bathroom was and he was not in there. And yes I did chill as I was walking down the hall to the bathroom,( I just thought there was a window open or something).  I went back to his bedroom and he was in there sleeping at REM stage.  When I saw him in bed alsleep, the hairs on the back of my neck stood up. I checked for REM just in case there was that possibility that I did miss him going back to his bedroom.  He would not have had enough time to return to the REM stage of sleep.  This was not monitor burn, where someone stairs at a tv or puter monitor and look up fast into the darkness and see images because when I saw the figure in his doorway I sat up a little to greet him and the figure stayed in the upright position.  

There you have it.  I have had other experiences too. 

Edited:  What in tarnation is a Rook??? Four years of college and I can't spell ROOM!!!

There could be the possibility that your son was sleepwalking. That happened once to me when I was about 12. I thought I saw my sis get up and walk into the kitchen but later I went to her room and she was fast asleep. You said the shadow was about his height. So maybe it really was him and he was just asleep.