Night Terrors, some kids have it worse than others and can take a long time to grow out of. Try not to let them have anything to eat before bed time as it can upset their stomach and make sleep difficult. Try getting a routine down where you make your son feel comfortable, read him a story, say a prayer...what ever you know that will make him feel safe and sound. Try putting a night light in his room, if he already doesn't have one, or let him sleep with his favorite toy or a special blanket.
My daughter is 3 and has these night terrors about 2 nights a week now, when it was every night but I did the things I just mentioned and it has helped us. She doesn't wake up from her dreams though, she will scream and cry and sometimes sit straight up. It is scary, and I know how you feel.
If it's to the point you are worried he's not getting a good nights sleep talk to his doctor.