Vivid, horrific nightmares run in all the females in my wife's family. It seems to be genetic. My wife had a very traumatic childhood, but her sister who was separated from the family at infancy and had a very stable childhood seems to have the same problems. My wife's nightmares are every night, and there was one very emotional period of her life where she would get up in the middle of the night and run around while still stuck in her nightmares. Her nightmares aren't what I'm posting about.
We have a 6 year old son, who turned diabetic at age 4. He's also had troubles with nightmares most of his life, and still requires tons of soothing and coaxing before he'll sleep alone. His most frequent blood sugar lows are at night while asleep. Since diagnosis, he's had two minor hypoglycemic seizures, both while asleep. Both times we were lucky that I happened to be near or in his room in the middle of the night when it happened.
After the second one I spent some wiki time on stuff related to seizures and hypoglycemia, and discovered that nightmares are a symptom of low blood sugars. Upon reading this, I recalled how both seizures began with him bolting upright in bed suddenly screaming in panic with the worst look of terror I've ever seen on his face. He then carries on like you'd expect of a kid stuck in a really bad nightmare for a couple minutes before the convulsions begin.
Discovering this + knowing my wife's seemingly genetic troubles with nightmares = me absolutely horrified anytime I think about it and try to process what he must experience at night