Actually, though the episodes are upsetting, they likely do not represent anything to worry about. They do not occur as a result of nightmares, but actually occur during a phase of sleep that is different from the phase qwhen dreaming occurs.
Children of your son's age experience, as a
normalNormal saline flush part of development, episodes of sudden partial wakings, during which they can behave in the way you describe. At these times your child is not really fully awake, and you should not try to wake him up. Simply do what you can to be reassuring, and 'guide' him back to sleep.
If you'd like to see more about these episodes, utilize our SEARCH function and type in Sleep Terror or Nighttime Wakings or Night Terror or Sudden Partial Wakings and you can read additional notes about the topic.