When I was in college, I had a girlfriend who suffered from night terrors. It sounds to me like your son isn't have "night terrors", but having extremely bad dreams. I don't want to correct you on this and I'm willing to take downvotes for this answer (first one on THIS exchange).
Night Terrors are very common and seem to be hereditary. The person who is suffering from a night terror is usually being held down by a gremlin (in their dream) and are paralized with fear and the pressure of this gremlin. The aren't able to breath as well because of the same gremlin. People have reported seeing a white horse (A "Night Mare") in their dreams and also someone standing over them, usually at the foot of the bed or in a door who they say is "death himself".
What's most fascinating about night terrors is that this is a recurring theme between cultures throughout the world, people who don't know eachother have the same dream. There have even been amazing pieces of art depicting this.
Anyways, enough of the history lesson. While I was with my girlfriend, I did a little research and studying. I came up with a way to stop her night terrors INSTANTLY. I did some research on her and found that her night terrors would normally last 3 minutes before she would start trying to scream out in her dream, which would come out as loud whimpers and moans. My test involved waving a card sprayed with a scent that she had a strong affinity for over her nose when she started to have a night terror.
In her case, she had a very strong GOOD memory when she smelled Curve Cologne. She thought of me, who would keep her safe. She explained that when I waved the card over her nose, the night terror would INSTANTLY go away and she would start dreaming of me instead. I knew, at least, the night terror would go away because I could see and hear her settle down immediately. She would relax (still asleep), no whimpering, moaning, etc.
Since then, I met my wife and found that she had the same night terrors. I did this same experiment with her with the same instant success, though with a different scent.
Now, about your son. The advice given already is amazing. I wanted to give you some of my studies and research. This may require some work on your part, where you will have to stay in your son's room until he starts having a nightmare then wave a strong specific scent in his face. Does he have a good memory to your parfume, oranges, cut grass, etc.? when you notice him tossing and turning, wave a scent over his nose. If he's anything like my "experiments", he should settle down right away. Eventually he won't be afraid to go to sleep, and possibly may train him to think of those good things while he's asleep.
Another thing I was able to help my wife with is when she was having a bad dream (rather than a night terror), I was able to get her to just "wiggle her toe". If you can remember the simplest little thing ("wiggle your toe"), it's a good way to start lucid dreaming. The advice above about your son knowing what to do in those situations would be great, especially if he can start to lucid dream. If you can teach him to control his dreams first, then he can start to be a super hero (suggested from another post).
Good luck with this. My son is 1 year old and I'm sure I will be dealing with this soon.