During night terrors, children commonly scream and jump right up from lying in bed. They may seem agitated, confused, and cry inconsolably. They may breathe more quickly, their heart may beat faster, and they often sweat. There can be a glassy-eyed stare as they are in REM (rapid eye movement) deep sleep and not actually awake. Be reassuring! There isn't much you can do other than protect your son from hurting himself. Once things settle down, he should usually fall right back to sleep and not remember what happened in the morning. This makes sense because he's never actually awake during the episode.
Nightmares, on the other hand, are scary dreams followed by full awakening. These happen later in the night and your child often will have difficulty falling back to sleep because of fear. He's aware that you are around and this comforts him. In the morning, he remembers the scary dream and can talk about it.
Usually night terrors go away on their own as your child gets older without any medication. Although kids can experience these on several occasions, it's much less common for night terrors to reoccur frequently or for long periods of time. You might want to speak with your son's pediatrician to see if she suggests other management options.