Sleep researchers conclude that, in most cases, sleep paralysis is simply a sign that your body is not moving smoothly through the stages of sleep. Rarely is sleep paralysis linked to deep underlying psychiatric problems.
If by the term "sleep paralysis" you mean the feeling of being awake yet totally unable to move a muscle, this is something that I have suffered now and again throughout my life. There are no negative consequences.
When we sleep, the body produces a chemical which keeps our muscles from moving so that when we are dreaming of running or jumping or diving or swinging a baseball bat or throwing out a fist, our bodies remain immobile so that we don't hurt ourselves or those around us. All mammals, I believe, are the same as us. It's a natural process even if it can be quite terrifying. I once saw a video of a science experiment where a kitten was deprived of this particular chemical and while the kitten was sleeping on his side, his legs were going a mile a minute because, it seems, the kitten was dreaming of running.
As to bad dreams, we all have those.
Have your son read the information at the link I sent. And you can search for more as well.