My middle child, Emily, has night terrors. It is, indeed, far more upsetting for the family who has to witness it, than to the sleeper, who does not remember any of it.
To answer your first question, is this from a past life, all I can say is, who knows? Maybe. Some elements of it could be. But, from what I have witnessed, Terrors are first and foremost a dream, a nightmare from a very deep, intense, dream state. The past life might not have played out exactly the way the Terror seems to show it to have been, so take some comfort in that.
Now, on to your next question, what to do?
If this is a past life being replayed in your sons head, then the best thing you can do, is let it play out to its conclusion. Keep your son safe, of course, but let him dream it out of his system.
Sorry. I know that is not what any parent wants to hear. We have tried other things, as well.
We have tried the blue light. It may have helped a little bit.
Honestly, though, what helped the most was removing blankets and making sure that Emily was not too hot as she slept. She would go to sleep cold, but warm up fast while she slept. The heat, I think, was the trigger for her mind to re-create it in her dream as panic.
We also tried talking to her in a calm voice, reminding her she was safe, while she was still awake / while asleep (I think you know what I mean by that. Anyone who has seen it, knows.) and reminding her of something happy. I like to think these moments helped train Emily how to direct her own dreams so the Terrors and nightmares happen less frequently now.
We also talk about it in the morning. She still can not do it, but I am helping Emily to learn how to control her dreams while they are occurring - lucid dreaming.
Lastly, and I am sure you have done this, but it bears repeating for anyone else who might be having similar problems but is too shy to ask...
Look for the physical triggers and try to remove them, especially before bedtime. Sugar, caffeine, energy drinks, medications, exercise, even video games can make the mind and body over-active and cause troubled sleep.
Hope this helps.