Nightmares begin occurring in most people before the age of 10. They’re normal unless they significantly interfere with sleep, development, or psychosocial development. What causes nightmares? Triggers are often correctable—especially in the cases of pre-bedtime eating habits and medications.

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You may remember, as a kid, occasionally waking up in a cold sweat, startled out of your slumber by one of those frighteningly vivid nightmares. Perhaps the experience still pops up from time to time; bad dreams may be more common in children, but adults aren’t immune to them. Around 85 percent of adults report having at least one nightmare in the past year, while 8 to 29 percent of us have monthly nightmares. Either way, those startling dreams beg the question, “What causes nightmares?”

It would help to understand what nightmares are. Unfortunately, there’s more mystery than quantifiable fact surrounding nightmares. For now, here’s what we do know about these “stories” that play out in our minds while we sleep: They’re “lengthy, elaborate dreams with imagery that evokes fear, anxiety, or sadness,” as Psychology Today puts it. “The dreamer may wake up to avoid the perceived danger.”

Nightmares are unique to each of us, they’re personal, and they’re so fleeting that we often don’t remember much about them. And there are any number of factors that trigger them. What causes nightmares for you, however, may not have the slightest effect on anyone else.

What Causes Nightmares

So what causes nightmares? Here are seven common triggers:

1. Anxiety and stress: Worried about work? Stressing about a relationship? Such common issues can manifest themselves in sleep-depriving nightmares.
2. Depression: Mood issues related to such life changes as divorce or break-up, death of a loved one, financial woes, and career concerns can lead to nightmares in some of us.
3. Eating before bedtime. That late snack increases metabolism, causing the brain to become more active, leading to more dream time. And a study published by International Journal of Psychophysiology reported that spicy food and junk food (candy bars, ice cream, and other sugary treats) trigger more brainwaves. A study published in The Journal of The Mind and Body showed that seven of 10 participants had nightmares after eating junk food just before bedtime.
4. Lack of sleep: Overtired from sleeplessness? That very condition could cause even more sleeplessness in the form of disturbing nightmares—a vicious circle.
5. Sleep disorders: Restless leg syndrome, twitching while sleeping, sleep apnea—all of these types of conditions can bring on nightmares.
6. Medications: Some prescriptions (antidepressants, for example) affect brain chemicals, so nightmares you’ve been having could be related to medications you’re on.
7. Withdrawal: Giving up medications (including sleeping pills and antidepressants) or substances (including alcohol) also can result in nightmares.

Haunted by Nightmares?

The Academy of Sleep Medicine describes nightmares as “recurrent episodes of awakening from sleep with recall of intensely disturbing dream mentation, usually involving fear or anxiety, but also anger, sadness, disgust, and other dysphoric emotions.”

If you’re worried that nightmares are a warning of some sort, relax. Don’t take them literally. In nightmares, we feel like we have no control over the imaginary scenes that are playing out, but they’re just that: imaginary. However, they do often reflect fears or obsessions.

According to Dreams.co.uk, the 10 most common bad dream themes are:

1. Our teeth falling out
2. Being chased
3. Being unable to find a toilet
4. Being naked in public
5. Being unprepared for an exam
6. Flying
7. Falling
8. Being in an out-of-control vehicle
9. Finding an unused room
10. Being late

Are Nightmares Bad for Our Health? The Surprising Answer

If nightmares are recurrent enough, they can develop into what’s known as “nightmare disorder.” The Diagnostic and Statistical Manual of Disorders defines nightmare disorder as “repeated awakenings with recollection of terrifying dreams, usually involving threats to survival, safety, or physical integrity.”

Fortunately, nightmare disorder is rare. However, there’s no doubt that recurring nightmares also may cause fatigue. We may have difficulty falling back asleep after nightmares because of their disturbing nature. In a classic domino effect, the fatigue can carry over into our work performance and/or interfere with family or social life.

But there’s a flip side: Research also shows that bad dreams actually may be helpful in getting us to move beyond a traumatic event. Nightmares can serve as an emotional release from anxiety that may be weighing on our minds; in fact, they’re normal reactions to stress we’ve been experiencing. “We think nightmares are so common that they have some purpose to process stressors,” Anne Germain, director of the Sleep and Chronobiology Center at the University of Pittsburgh, told CNN in 2017.

Being haunted even by traumatic events may be helpful, research shows, and experts think they could actually be beneficial. “Nightmares in the first few weeks after a traumatic event have not been associated with health problems,” reported CNN’s Carinna Storrs.

One study illustrates that more than 20 percent of women who were victims of sexual or physical assault were experiencing nightmares about the event three months later. Another study shows that survivors of serious car and motorcycle accidents also were having nightmares months later.

This article was originally published in 2018. It is regularly updated.