Flower Your poor GS. That must be terrifying for him if he is seeing his room changing shape. And it must be terrifying for his mum to see him having the night terrors. My DS had them as a baby, although we got told that babies don't have night terrors. Well, he wanted to come and see him then. He would scream as though being hurt, suddenly, no build up. Then when we held him he would look straight through us, as though he couldn't see us. And he was sleeping in my bed with me only, (hubby on settee) from being born until about four years old.
We used to get up with him, sit him with one of us and put Thomas on the tele until he recognised him and then he would come round and we could talk to him then. It was a very scary time. Could he have a tele in his room with a sleep timer on that could be set with a dvd in it? I would want to see that they have come out of the terror though so I don't know if this would be ok. Maybe try putting his baby sister in with him. Or there is a clock I've just looked up for you, Gro-Clock Sleep Trainer which has a light on and moons and the sun and teaches youngsters when it is ok to get up when the sun comes out and to stay in bed when the moons show. It's on Amazon, check it out. Maybe it would help.
Now my son is 17 and I have trouble getting him out of bed! He also used to go from totally asleep to crawling on all fours towards the wall in a second. I put a mattress against the wall to prevent him knocking himself out. It was an horrendous four years and not time I would ever want repeated, not the sleeping part anyway. Now, thankfully, I get all the sleep I need.