Close encounter, or just half asleep? How scientific inquiry can inform paranormal experiences

By Laura Reyes
October 15, 2014

Since it’s getting close to Halloween, I thought I would discuss something a little more creepy than usual that actually happened to me. I had just finished a late night working on an abstract, and was peacefully drifting off into sleep. I was so happy to finally be in bed, asleep. I floated through a few different dreams, none of them particularly interesting or memorable. I’m pretty sure one of them involved waiting for a couple hours at an airport.

Suddenly, I felt an undeniable sense of dread. There was a presence to my left. It didn’t feel like someone I specifically knew, but more like someone I knew of…and I somehow knew I should be afraid of them. In the dream, I tried opening my mouth to scream, but nothing came out. I woke up a bit and realized I was at home, in bed, and I tried moving but I couldn’t. I tried screaming again, but I was totally paralyzed. I tried opening my eyes, which at that point were still closed, but my eyelids were too heavy and refused to budge. I felt stuck…stuck and terrified.

Finally, after what seemed like half an hour, I managed to open my eyes. My eyelids barely moved at first, but when they finally opened I wished they hadn’t. The wall across from my bed had dematerialized and formed what I can only describe as a portal. Through this portal came a white being. It was foggy at first, and drifted toward the foot of my bed. As it neared me, it began to take a more definite shape. Little by little, I could make out legs, arms, and eventually a head. The head also started to become more apparent, and I glimpsed a pair of dark eyes glaring at me. “This is it,” I thought, “it’s finally happening. It’s here. IT’S HERE.” As I writhed around in my bed trying to get away, the haze of sleep gradually lifted. The terror from the previous moments was still fresh in my mind and I didn’t know what was real and what was just a dream. The area where the portal had been was still darkened and the wall appeared unstable. It took about 10 minutes before I felt grounded in reality again, and this reality was grim. I had experienced a visitation from an interdimensional alien.

…or had I?

Because I study evolutionary neuroscience, I find I am particularly interested in how the brain is involved in paranormal experiences. I have had more than a few of these experiences and always wonder what’s really going on. I’m obviously not the only person looking for an explanation because there are countless websites and message boards dedicated to the events that are perceived as alien visitations and abductions. Even before the internet, such stories were told through books and movies. But could there be another explanation?

Take one look at art throughout the ages and you’ll find that this type of experience pre-dates our society’s current obsession with alien visitors. Countless sculptures and paintings from the western world depict incubi, succubi, or demons standing over, and sometimes sitting on the chest of, their sleeping victims. Even groups from disparate places like Turkey, Nigeria, and Fiji report visitations from demons that appear to strangle or hold people down while they are sleeping. This experience is common in my own family, as well. Both my mother and grandfather have felt these types of sensations during sleep, and refer to them as pesadilla, the Spanish word for nightmare.

Henry Fuseli, The Nightmare, 1781. Detroit Institute of Arts.

Recent research on sleep has shown that these types of experiences are relatively common, and are known as sleep paralysis. Sleep paralysis is linked to a malfunction in how the brain controls the different phases of sleep. During sleep, the brain goes into different stages, alternating between rapid eye movement (REM) and non-rapid eye movement (NREM) sleep (Silber et al., 2007). When we first fall asleep, we pass through NREM stage 1 sleep, a kind of fuzzy state of consciousness between being asleep and being awake. Next, we pass through NREM stage 2, where it becomes a lot harder to wake up. NREM stages 3 and 4 occur next, and in these stages we are very difficult to awaken and only respond to the most salient stimuli from the waking world. After these deeper stages are reached, the brain will enter REM sleep for short periods of time, and will return to NREM stages of sleep in alternating periods, as seen in the figure below. During REM sleep, brain activity resembles the activity during wakefulness. There are bursts of brain activity coupled with rapid eye movements, though body muscles are paralyzed. REM sleep is often called paradoxical sleep because it’s very difficult to wake someone in REM sleep, but yet the brain appears almost fully awake.

REM sleep is also the part of sleep when we have experiences that we remember as dreams. The high activity seen in the brain reflects the awareness we usually feel while dreaming, while the muscle paralysis keeps us from acting out our dreams (Gugger and Wagner, 2007). Sometimes, though, REM sleep doesn’t unfold as it should. Although the exact mechanisms of sleep paralysis are still unknown, it seems to occur when there is an overlap between REM sleep and awakening (Kristo, 2005). If sleep and wake cycles aren’t properly regulated in the brain, the physiological effects of REM spill over into brief periods of awakening at night, leading to a relatively alert brain and an unresponsive body. Hallucinations also occur often during sleep paralysis, and might come from parts of the brain still producing dream imagery even though the brain is generally awake. Sleep paralysis literature also refers to a phenomenon called “the intruder,” which parallels the description of a menacing presence in the room. This feeling of terror might come from a defensive mechanism of the brain as it reacts to being awake and paralyzed while experiencing dream-like hallucinations (Cheyne, 2003).

I know, right? Sleep paralysis sounds really weird, and maybe seems like something that doesn’t happen enough to account for all of these stories of demons and aliens throughout the ages. Sleep paralysis does occur most often in people with existing sleep-related disorders, such as narcolepsy and sleep apnea, and there may also be a genetic component to sleep paralysis (Taheri and Mignot, 2002; Dauvilliers et al., 2003). However, a 2011 review of 35 sleep paralysis studies taken from English and Spanish language journals showed that 7.6% of the general population has experienced sleep paralysis at least once in their lifetimes (Sharpless and Barber, 2011). It tends to affect people who experience a lot of sleep disturbances or don’t get high quality sleep (oh, you know, like students, people with kids, people with jobs, people who like sleeping with their computers/iPads/iPhones in their bed). The onset of sleep paralysis is also affected by sleep position and occurs most when a person sleeps on his/her back (Cheyne, 2002). My mom actually used to tell me all the time never to sleep on my back with my arms on my chest or I would get pesadilla…so there might actually be some truth to that.

I’m obviously not the first person to link demons and alien visitations to sleep paralysis (McNally and Clancy, 2005). This notion has been considered in the psychological literature for a while, and is part of a larger trend toward finding testable hypotheses and natural explanations for paranormal experiences. I think this is actually what we should all be doing. We should reflect on our experiences and ask ourselves what is really going on and consider whether or not we are using science and research to come to a conclusion.


Cheyne, J. 2002. Situational factors affecting sleep paralysis and associated hallucinations: position and timing effects. Journal of Sleep Research 11: 169-177.

Cheyne, J. 2003. Sleep paralysis and he structure of waking-nightmare hallucinations. Dreaming 13:163-179.

Dauvilliers, Y., Billiard, M., and Montplaisir, J. 2003. Clinical aspects and pathophysiology of narcolepsy. Clinical Neurophysiology 114: 2000-2017. 

Gugger, J.J. and Wagner, M.L. 2007. REM sleep behavior disorder. Annals of Pharmacotherapy 41(11): 1833-1841.

Kristo, D.A. 2005. Sleep Paralysis. American Academy of Sleep Medicine.

McNally, R.J. and Clancy, S.A. 2005. Sleep paralysis, sexual abuse, and space alien abduction. Transcultural Psychiatry 42(1): 113-122.

Sharpless, B.A. and Barber, J.P. 2011. Lifetime prevalence rates of sleep paralysis: a systematic review. Sleep Medicine Reviews 15(5): 311-315.

Silber, M.H., Ancoli-Israel, S., Bonnet, M.H., Chokroverty, S., Grigg-Damberger, M.M., Hirschkowitz, M., Kapen, S., Keenan, S., Kryger, M.H., Penzel, T., Pressman, M.R., and Iber, C. 2007. The visual scoring of sleep in adults. Journal of Clinical Sleep Medicine 3(2): 121-131.

Taheri, S. and Mignot, E. 2002. The genetics of sleep disorders. Lancet Neurology