S.D.
Hi L.,
If your son knows you are there when he is screaming, shaking and upset, it is probably not night terrors, though I am not a doctor and can't diagnose the issue. What I have done, and it seems to work, although it may sound like I am nuts, is to tell my son when I put him down for the night to "tell anyone that is not of God that they have to leave, and ask God and his angels to watch over him and protect him from anything that might scare or harm him, and to keep him safe". I also have a Herkimer Crystal (a naturally faceted quartz crystal, a regular quartz crystal is ok too if you choose to use a crystal in conjunction with the "prayer")that I have in his room and clear it when the "prayer" doesn't seem to be working so well. It's worth a try, it can't hurt anything or anyone, so even if it sounds crazy....Hope this helps.