Night terrors have tormented us as a race from the START of the race. But they aren't the most frightening form of nightmare to me. The most frightening would probably be what's called "sleep paralysis." I've never suffered from this type of nightmare, but plenty of people have... it's the type of dream where you wake up, hallucinate, and simply can't move... and all that comes with an overwhelming feeling of terror and dread. It's from experiences like these that all manner of notorious legends and myths have evolved, from the succubus and incubus on up to the more contemporary aliens who supposedly abduct folks to perform experiments.
One such creature in this category is the alp—a creature from German mythology similar in some ways to a vampire, in others to a ghost, and in still more to an incubus (although the legends generally don't include a sexual element in the alp's case).
Yet, if I've never had sleep paralysis before... why am I suddenly all intrigued by alps? Well, I just finished playing a VERY good video game earlier today—a tense and stressful thing called Outlast. In the game, you play a reporter who gets a tip that there are strange goings on at an old asylum, and so you head up there one night to investigate, armed only with your video camera. This camera is also your only way to navigate the darkest parts of the asylum, by letting you use the night-vision mode to do so. Of course... there are ALL SORTS of horrific things going on in the asylum for you to run from and hide from; crazy people, deranged doctors, naked deranged orderlies, deformed lunatics, mutants... and as the game progresses, something called a "walrider." Which is, of course, another name for the alp.
The game's a piece of work. Made me jump back from the computer several times. Highly recommended. Just don't play it late at night, especially if you're prone to the terrors! Check out the gameplay footage/trailer below... IF YOU DARE!