Greetings!
As for answers, the entire human race have been seearching for specifics for thousands of years:) However, I offer a suggestion. Sleep next to him one night or two. Observe if he has the same experience in contrast. If the behavior is still the same then experiemnt more. Before bedtime give him a massage, work the enviroment with music. Create a loving enviroment with peaceful additions. Think out of the box here. Also, record his behavior each night in a notebook. You have a question "is my son haveing night terror?" Every single scientist has a question. They conduct experiemnts to figure out the answer. They collect data/information over a period of time. They observe. If this keeps happening you can take him to the ER or Doctor/ specialist and have them conduct tests with high technical equitpment, however, you can do one thing they won't do...explore your imagination and create various ways to express love to him right before bedtime. Search infant/child massage and it's benefits...it's one way of expressing love. This is why I am suggesting this because in 1 corinthians 13 or so it says "Love never fails". Also, pray...before goes to bed and when he's asleep.
And I wish to say I do not have the answers, however, I would rather try than not.
The power of prayer is within you:)