Years ago, I woke to see a darkly cloaked figure towering over me. I thought it was going to kill me, but I couldn’t move. I wasn’t dreaming. I could see my room and feel my body beneath my sheets. I was consciously aware, yet hallucinating a figure that didn’t exist.

I was experiencing sleep paralysis, a phenomenon that affects approximately 30 per cent of people worldwide. Episodes are usually benign, but for roughly 1 per cent of people, they reoccur weekly, raising the risk of insomnia. Even isolated instances can leave a lasting impression. I still think about my experience today. While I know the figure wasn’t real, the fear it instilled in me was.

In his latest book, The Phantom Mind: Insights from the borderlands of sleep, Baland Jalal reveals how and why sleep paralysis can take hold. A neuroscientist at Harvard University, his research has brought us closer to understanding what affects the appearance of so-called “sleep paralysis demons” and how we can potentially prevent these frightening experiences. Jalal sat down with to discuss what all this tells us about the mind-body connection.

Grace Wade: I am curious – have you experienced sleep paralysis?

Baland Jalal: I have. I had my first episode when I was about 18 or 19. I was sleeping and suddenly realised: I am awake, yet I can’t move. I can’t speak. I felt this looming presence, this shadow-like creature approaching me. And then it strangled me. It pressed on my chest, and I saw my legs flying up and down. I was sure I was going to die. But eventually, I managed to wrestle myself out of it. It was a horrifying, but also life-changing, experience because this was the trigger for me to become a scientist.

That sounds awful. What happens in the brain during this phenomenon?

Sleep paralysis emerges out of rapid eye movement (REM) sleep, when we have our most vivid dreams. During REM sleep, we are completely paralysed from head to toe so that we cannot act out our dreams. What can happen is that the outer layer of the brain can suddenly activate and jolt you awake while you are still in REM paralysis.

We know what can trigger this. Deep in the brain, you have the limbic structures, the emotional department of the brain. If you are aroused during the day – you have a lot of anxiety, a lot of stress – that part of the brain is hyperactive. When you go to sleep, it will stay activated and sort of tickle the outer layers of your brain, and you jolt awake. Now, if the emotional part of the brain wakes you when you are supposed to be in REM sleep, you have sleep paralysis, because you can’t move.

But why do people see or hear things that aren’t there?

Sleep paralysis is really being awake and asleep at the same time. And what happens in REM sleep? All these parts of the brain are turning on and off, and that creates a surreal dream world.

For example, the dorsolateral prefrontal cortex, the rational part of the brain, shuts down during REM sleep. It puts the world together in a logical way, and for that reason, dreams are bizarre. The cingulate cortex, which has to do with conflict monitoring and empathy, is hyperactivated during dreams. It is why we can create theory of mind, meaning we can project agency and intentions onto other beings in our dreams.

The temporoparietal junction, which creates a sense of body image, also takes a hit during REM. So your sense of self is all fluid. And then the emotional part of the brain, the limbic structures, is about 30 per cent more active in REM than when awake. That explains why dreams are so emotional, so intense.

Now you have sleep paralysis, where you start waking up, yet these elements of the REM dream are spilling into waking reality.

How do we know this?

In terms of the brain regions that turn on or off during REM sleep, that comes from brain-imaging studies. In terms of why we see monsters during sleep paralysis, that is all theoretical. It would be interesting to conduct brain-imaging studies of people while they see [them] to find the exact neural pathways that light up. You might think that isn’t important, but I think it could be. It might show us the pathways governing extreme dread, religious fear and mysterious experiences.

Why haven’t we done that? I imagine capturing sleep paralysis with a brain scanner would be challenging.

I don’t think it would be that challenging. You would have people that are already predisposed to sleep paralysis and then disrupt them during REM sleep with a scanner on.

I think the reason it hasn’t been done is because, in most cases, sleep paralysis is benign. It would be hard to get grant money.

In your book, you suggest that sleep paralysis is a unique window into consciousness. What do you mean by that?

You have the dreaming brain, with all these different parts being shut down or hyperactivated, and then it blends with the waking brain, where you have some conscious awareness. I think that gives us a potential window into understanding aspects of consciousness.

The ability to choose is a key aspect of conscious experience. If you were able to communicate with someone in sleep paralysis and ask them to choose, say, Pepsi or Coca-Cola, they would be able to. Compare this with sleepwalking. From the outside, that person might look conscious, but they aren’t because they cannot choose.

Sleep paralysis has shown us that mixed states of consciousness are possible and that you can have some self-agency in these states. I think one of the most important insights is that your own mind can potentially trigger an event that seems comparable to trauma.

We also know that if you have a certain cultural idea about sleep paralysis, it becomes more common and it seems to last much longer. That is a big insight of the mind-body connection.

Your research has focused on the role beliefs and expectations play in sleep paralysis. Tell me about those findings.

After my sleep-paralysis episode as a teenager, I decided to become a scientist and study it. I went to Egypt, got into The American University in Cairo. I am originally from Denmark, where we have very secular views. Everything is as you see it. Egypt, on the other hand, is a very superstitious place. So I thought, how would sleep paralysis differ in these two cultures? And it differed quite severely.

My colleague, David Hinton at Harvard, and I surveyed hundreds of people in Denmark and Egypt, asking them whether they experienced sleep paralysis and, if so, what it was like. About 90 per cent of people in Denmark said it is just your brain. It is stress. It is physiology. Nothing supernatural about that. The people in Egypt were completely different. They would say it is a genie – evil genies, not the nice blue one from – and they feared it intensely. About 50 per cent of people who had sleep paralysis [in Egypt] thought they might die from it.

And this seemed to influence their experience of sleep paralysis. So, people in Egypt would say their episodes last much longer [than people in Denmark]. It was also twice as common in Egypt than in Denmark. We think that has to do with how the idea spreads from person to person.

I was once told that you can only experience sleep paralysis after learning about it from someone else. Then, boom! I had my first episode.

That isn’t the only way, but it definitely becomes more common, which has to do with a phenomenon called priming. This is how it works. Let’s say you have this girl who has never heard about sleep paralysis. Then, her grandmother warns her of these monsters that come at night.

Now what happens? She goes to bed and the emotional core of her brain is hyper-alert, which is this perfect disaster for sleep paralysis, because you are so likely to jolt out of REM. Then, in REM, she feels something holding her down, which is just her brain paralysing her. When she tries to move and can’t, she panics. Then her dream imagery will create these vivid hallucinations. She wakes up terrified, tells her friend and the scenario starts all over. It keeps spreading.

This is a personal question, but what form does your sleep paralysis demon take?

It has evolved. My first encounter was a shadowy sense of presence. It was the most terrifying episode ever.

When I was in Egypt, it was during the Libyan revolution, and Muammar Gaddafi [the former Libyan prime minister] was on the news all the time. One day, I was sleeping and it was Gaddafi hovering over me. That was very spooky. Later, as a PhD student in England, I would go to these castle-like hotels to give talks, and they seemed so haunted. I would have terrifying episodes there.

So it isn’t only cultural beliefs that shape sleep paralysis, but also environment?

Absolutely. Terrifying castles? Terrifying sleep paralysis. Somebody who doesn’t know the neuroscience of sleep paralysis would think it is a haunted hotel. We have data from people reporting that if they have a poster on their wall, suddenly that would morph into a dangerous face, or a little glass on their table would morph into a skull. So the environment primes the experience, for sure.

Absolutely. I developed four steps people can do during sleep paralysis. It is very simple. First is a cognitive reappraisal, which is a fancy way of saying “reinterpret the whole thing”. Remember, it is just the brain playing tricks on you. Then, you do emotional distancing. Since you know it is the brain, it makes no sense to be scared. I may have those emotions, but I am going to distance myself from them.

The third step is key: you meditate on something positive, your mother’s face or God or the sunset, whatever is positive for you. That can make the frontal parietal part of the brain, the part that has to do with attention, bias the brain toward positive emotions. Number four is that you will still have paralysis. You can’t avoid those physiological symptoms, so ignore them.

We did a study with six people in Italy who had sleep paralysis frequently. Their episodes decreased by about 50 per cent after using this for eight weeks.

This is very promising, but very preliminary. We are now working on a follow-up study of this therapy.

Why is treating sleep paralysis important, given we know people aren’t actually being attacked by a monster?

Because of the pervasive nature of the experience, the way it spreads, the way it can harm people psychologically. Even having a few episodes a year can be destructive. And a small percentage of people have several episodes a month. That is when it is really pernicious and pathological. You just can’t get rid of it, and it is causing insomnia.

Have you tried this technique yourself?

A few times. It seemed to work. Sleep paralysis has evolved for me from being terrorised by this shadow-like creature to now [when] I can take control. I have learned to have my prefrontal cortex kick in and regulate some of the fear structures.