when he screams during the night, do you go immediately to him? is he fully awake? or just screams with his eyes shut? what do you do? do you feed him? or just a cuddle?
my DS sometimes cry out in his sleep, may be dreaming, before i go to him, he fall back to sleep. if my DS is waken by something, he can usually put himself back to sleep by chewing his blanket. (always found blanket in his mouth). so how does your DS fall asleep? do you know? if not, may be spy on him, it might help you.
or do you think it's comfort factor? we have heater on throughout the night as we have quite a cold and drafty room. i figure out if i have the heater on all night, it will be very drying and very hot towards the morning. so i put a timer on and off each hour, and hang some wet towel in the room. otherwise DS will wake middle of the night due to thirst.
all i can think of at the moment. hope there will be more suggestion coming in.