The only thing I would suggest in order to help you feel calmer about it is that you perhaps test his blood sugar when he wakes up screaming just to make sure he is neither terribly high or terribly low. If not, then diabetes probably has nothing to do with it. If he drops too low, he probably will wake up, and screaming is sometimes how a child who is low lets you know. I personally (I am the diabetic in my family) know that if my glucose levels rise too high, I will wake up, also. So you may want to test him just to be sure that glucose levels have nothing to do with the situation.
My son does the same thing. I am diabetic not my son. We call them night terrors. He seems to be growing out of it. It used to happen at least 2 times per week and now it is every month or even less. They started when he was just turning 2 and now he is four. It seemed to start when his sister was born. He would scream and cry and would scare us to death and then he would wake up and be fine and go right back to sleep.
Hello again! I'm not a medical professional, just the parent of a child with diabetes, like you. It kind of sounds like symptoms of sleepwalking. Is he in growth spurts or anything which might be affecting his ability to sleep well?