What are nightmares, and why do we have them? Patrick McNamara, an experimental neuroscientist who studies the neurobiology of sleep, dreams, and religion, believes nightmares have both important spiritual and emotional functions for our minds.

While nightmares can be deeply unpleasant, they have been experienced and recorded by humans for thousands of years, and historically those who were able to withstand and control their nightmares were held in high societal regard — appointed as spiritual guides or shamans.

Beyond the spiritual, McNamara explains that nightmares can provide insights into the neurobiology of our REM sleep, where we can confront and process trauma. Nightmares can create a kind of exposure therapy, assisting emotional regulation and helping to maintain healthy emotional responses to the environment. That’s why REM sleep is crucial for processing trauma: It allows us to integrate traumatic experiences into our long-term memory stores.

Patrick McNamara: So I've been arguing that REM sleep is crucial for religious consciousness and for human creative capacities and for human cultural evolution, but when it goes off the rails, it's associated with a lot of very serious disorders as well: everything from depression to isolated sleep paralysis and nightmares in particular. Now a "nightmare" is defined by most sleep medicine specialists as simply a scary, terrifying dream that wakes you up. A lot of other sleep medicine specialists say, "Well, it doesn't need to wake you up." If you have a really terrifying dream, that's a nightmare. And we know that nightmares tend to occur during REM sleep. And we know that lots of kids go through a phase where they have lots of nightmares, and then they sort of disappear for most people. But the people who are vulnerable to nightmares have sort of a disinhibited form of REM neurobiologies. REM tends to erupt into their waking consciousness, a little bit, and they get these dissociative states during the daytime, and, unfortunately, nightmares during the night. 

So, nightmares for the most part, there's nothing good about them, and I just wanna underline the fact that there are very good treatments. You don't have to suffer from nightmares. But from the point of view of somebody investigating religious consciousness, nightmares are particularly important because for most people who have nightmares, supernatural agents appear, and for many of them, particularly for people with religious backgrounds, those supernatural agents will be demonic agents. And unfortunately, those demonic agents really have very specific, enduring effects on this person's suffering from nightmares. 

There are many examples, but when you look at series of nightmares over time, one common pattern is that before the series of nightmares begin, a demon appears just in the room. The person has a nightmare and they say, "I woke up from the dream and, wow, there's this weird demon in my room. But he was just there, he wasn't doing anything. It scared me, and I woke up." And then a week later, they'll have a very similar dream with the same demon, and the demon will now be near the bed. No longer in the corner of the room, but near the bed. The third week I have the nightmare again, it's a very similar nightmare, and now the demonic agent knows that the dreamer is aware of them, and so the demonic agent ups his game and tries to get closer and closer to the individual having the nightmare. And so the individual starts to put up barriers to protect themselves. In an individual who's particularly vulnerable to nightmares, these barriers will eventually not work. And they need to get clinical help before that happens because in many cases, the demonic agent is out to possess the individual's consciousness. And the individual will wake up.

I mean, if you look at case studies of demonic possession, they invariably occur after a series of nightmares and then finally the demonic agent in the nightmare possesses the individual's consciousness, and they wake up in a possessed state. And then you need, you know, like, exorcism rituals to get rid of the demonic agent. So those are some of the ways in which nightmares teach us about supernatural agents and religious consciousness, and why, obviously, you do not wanna have nightmares. However, nightmares have been around, we're almost certain, for many thousands of years.

We have evidence that people who experience frequent nightmares but are able to control them and able to control the demonic agent in traditional tribal societies gain great social status, 'cause who can be more powerful than a person who can control a demonic agent? The nightmares mark them off as special human beings that the divine has called them in a special way, and only somebody who's strong enough to deal with those demonic agents are called to be a shaman or a spiritual guide for others. So, that's how people with nightmares in traditional societies were held, you know, in special, high regard because they carried this special burden. 

So, nightmares tell us a lot about religious consciousness, and about REM neurobiology. One of the things they tell us about REM neurobiology is REM has special, computational, neurological machinery to handle trauma. We think that the fear extinction circuit in REM sleep functions differently during a nightmare than during a ordinary dream, and the reason why the fear extinction circuit, the computational machinery that's used to handle emotional traumas, doesn't function well is that the fear extinction circuit breaks down at a certain gate — it's blocked for some reason in some individuals. And because the brain uses REM sleep to handle traumas, and when that trauma can't be handled effectively, immediately the trauma memories hang around in REM sleep, and you get PTSD. So, every night the individual continually tries to integrate the trauma into long-term memory stores and then get rid of it. And that's why REM is so crucial for getting through calamities and plagues and all kinds of horrible events because it's nature's special way to handle emotional trauma.