Oh, welcome to my world! (lol) My daughter, now 5 1/2, has been having night terrors for a good year now- at least. She wakes up almost every night- screaming, sometime tears running down her face, often sitting on her knees on her bed facing the corner of her room. FREAKY!!! But when you talk to her- her voice instantly becomes calm and sweet and she swears nothing is wrong... obviously still not awake- but no longer scared. She never remembers anything the next morning (thank goodness). Just recently she started walking in her sleep. We have decided to put a chain-lock thing at the top of our doors that lead outside of the house, just to try to keep her a little more safe. Her Dr. also said that it can be a totally normal thing and that we are going to just have to ride it out- probably into early adolesence!
There are times that it gets worse, for instance if she is not feeling well, or if she didn't get a nap earlier in the day and is perhaps overly tired... all kinds of things. But quite often these experiences happen when there is no clear explination.
Just hang in there, keep talking to him, and do what you can to keep him safe.
From one Mom to another, good luck! ;)