No matter how serene your sleep may usually be, chance are you’ve experienced a nightmare or two. These haunting dreams are often elaborate, lengthy, and full of imagery so terrifying they can cause you to wake up in a cold sweat. In fact, one of the hallmarks of nightmares is that they wake you up, and can keep you awake for hours.

While it can be fun to interpret more pleasant dreams, figuring out the meanings behind nightmares can feel particularly pressing due to their intensity and vivid symbolism. What does it mean to see a shadowy demon under your mattress night after night? And why is it that so many of us dream of losing our teeth when we’re stressed?

Note: The content on Sleepopolis is meant to be informative in nature, but it shouldn’t take the place of medical advice and supervision from a trained professional. If you feel you may be suffering from any sleep disorder or medical condition, please see your healthcare provider immediately.

Dream Interpretation

The earliest evidence of dream interpretation dates back to 3100 BC, when priests in the ancient civilization of Mesopotamia divined supernatural insights from the nighttime visions of kings. In Egypt and Greece, dreams continued to hold a prominent place in the collective consciousness, with royals and laypeople alike seeking guides to help them understand their dreams and nightmares.

As the centuries passed, dream interpretation moved away from mysticism and found new roots in science. Scholars across China, the Middle East, and Europe studied the phenomena, but it wasn’t until Sigmund Freud published his groundbreaking book The Interpretation of Dreams in 1900 that modern psychology tackled the subject. Though the book has since been mostly debunked, Freud”s theories inspired a new generation of researchers to investigate why and how we dream.

What About the Really Scary Ones?

Experts have yet to agree on what nightmares mean. Though causes can range from stress to fever to medications, the significance of nightmares is less clear. However, there are some popular interpretations associated with the most common types of frightening dreams. Here are eleven of our favorites:

Want to learn more about dreams and nightmares? Read all about the symptoms, causes, and treatment of nightmares, as well as the purpose of dreams. And check out our guide to lucid dreaming, and don’t forget our comprehensive overview of dreams of all kinds, What are Dreams?

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