Melatonin and Cortisol are a pair of tom cats prowling in the dark alleys of our minds.
Occasionally they get into a (fight) but not until one takes (flight) does the fracas cease.
Ps
I suffer from night fear so I write from experience. In my case, it is not terrors whilst sleeping, this occurs when I wake. Robin Williams suffered from it as do millions of people. Research what Williams wrote on his AA book, google it.