Edgar Allan Poe was known for his bone-chillingly terrifying stories.
Many of these tales were influenced by the horrific nightmares that plagued him for most of his life. Poe explored the mysteries of these chilling dreamscapes in poems like "Dream-Land," in which he described wandering down "a route obscure and lonely/ Haunted by ill angels only."
Most people, thankfully, don't live their lives haunted by the kind of sinister night visions that Poe experienced. But most of us know that the mind at rest can travel to some pretty strange (and sometimes disturbing) places.
Nightmares are relatively common and in most cases a healthy psychological experience. Most people experience them only occasionally, but roughly 6 percent of adults have nightmares on a regular basis.
A nightmare, which typically occurs during REM sleep and feels very real, is something more than just a bad dream. So what's really going on in your mind when you're having one?
"Nightmares are generally more emotionally intense than bad dreams, and usually how they're distinguished is that a nightmare will cause the person directly to awaken, either because of the nature of the unpleasant images or the intensity of the emotions," Dr. Zadra Antonio, a psychologist and sleep medicine researcher at the University of Montreal and a nightmare specialist, told The Huffington Post.
Here are five scientific findings about nightmares to help demystify your creepiest dreams.
Nightmares may be your brain's way of releasing anxiety.
Recurrent nightmares can be a sign of post-traumatic stress disorder or some other psychiatric health issue, but in most cases they're unrelated to mental illness. In fact, there's nothing wrong with having nightmares -- they might actually be good for you!
A video from New York magazine's Science of Us series, "The Good Side of Bad Dreams," explains that nightmares can act as a way for us to process and let go of our day-to-day anxieties. The mind does this by taking an abstract fear or worry and fashioning a story out of it. That story then becomes a memory that your brain can file away and be finished with.
In addition to fear, nightmares can give rise to a number of other negative emotions, including helplessness, despair, guilt and anger -- possibly allowing the mind to process these feelings as well.
Your nightmares aren't unique.
In a study published last year in the journal Sleep, Antonio and his colleagues at the University of Montreal collected nearly 10,000 dreams from 331 adults living in Canada.
Through these case studies, the researchers identified common themes that come up in people's nightmares -- and there's a good chance you've had at least one of them. Based on this and other research, psychologists have found that the most common nightmare themes include insects and vermin, falling, being chased, death of family and friends, interpersonal conflict and violence, feeling an "evil presence" and health-related concerns.
"Our nightmares pick up on universal fears that people have," Antonio said.
Trying to interpret your nightmares probably won't get you very far.
Sigmund Freud saw dreams as a window into the unconscious mind, and he was fascinated with dream interpretation. The Austrian psychoanalyst believed that all dreams carry information about subconscious (and often sex-related) desires and fears.
Since Freud's time, research has failed to support the idea that dream themes and symbols have universal meanings, and psychologists have all but abandoned the practice of dream interpretation.
So while it may be tempting to turn to that dream dictionary to analyze the images in your nightmares, it probably won't help you decode your dreams in a meaningful way, Antonio said.
"That's not to say that nightmares aren't meaningful," he added. "They certainly are meaningful and they are metaphorical, but the way they are presented varies greatly from person to person."
Men tend to dream of natural disasters, while women dream of relationship troubles.
Apocalyptic dreams of extreme natural disasters or asteroids wiping out the Earth's population aren't uncommon.
In the University of Montreal study, disasters turned out to be a common nightmare theme. Interestingly, the data revealed that men were significantly more likely to dream of catastrophe, with 9.4 percent of men and just 4.7 percent of female participants reporting this theme. Similarly, an earlier study found that men tended to have war and terrorism show up more often in their dreams.
Women, on the other hand, are more likely to dream about having intense interpersonal conflicts.
"Having really severe arguments with family, friends or colleagues is more common in the nightmares of women," Antonio said.
Nightmares are linked to some sleep disorders.
The biggest problem with nightmares is usually that they can impair sleep quality and cause next-day drowsiness. But in some rare cases, it can become more serious.
When nightmares are frequent and severe, the individual may suffer from nightmare disorder. This is a type of parasomnia, a class of sleep disorders that involve uncomfortable experiences while falling asleep, sleeping or waking up.
Other forms of parasomnia include sleep terrors, which cause the individual to sit up and cry out, or to attempt to escape the room, while still asleep. Sleep hallucinations, another rare nightmare-related disorder, occur when a person experiences intensely vivid images while falling asleep or waking up, resulting in feelings of fear or dread.
There are few things more unsettling than experiencing a full-on nightmare, with all the menacing imagery and bizarre dream logic that attend them. But the next time this happens to you, and you wake up in the middle of the night with your heart pounding, just remember you're not alone.