Hi Em--my son had night terrors as well; I think he was about 3 years old? It was really scary and it often would get worse if we tried to hold him. So we usually just sat in his room to be with him and let him ride it out. I don't think there is anything in particular that is scaring him (tho I'm not totally sure about that). I know that it was worse when he wasn't sleeping well and he went through a period of several weeks of not napping, getting up really early and just really screwy sleeping! So that is something to look into. My pediatrician gave me a cool chart to keep track of his sleep and that really helped.
Good luck to you!
HTH
Bea