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Ask anyone whether they’ve felt pain in their dreams, and you’ll likely be met with the same reaction: a thoughtful pause, a pensive look, maybe a hesitant and confused “I think so”. There’s that old cliché, after all — “pinch me, I must be dreaming” — that suggests physical pain in our dreams simply doesn’t exist. But ask psychologists today and the answer, at least according to scientific research, is decidedly yes: Even within the comforts of your dream world, sensations of physical pain — whether it’s getting sliced in a knife fight or bitten by a dog — can exist and feel devastatingly real.

The nuances of pain — such as why it happens, how it happens, and its purpose — remain much less understood, even to those who have hounded the subject for decades. “It never ceases to amaze me that the brain — while a person is asleep in bed cut off from the outside world — can create such complex and convincing worlds that we take as true,” says Antonio Zadra, a psychology professor at the University de Montreal’s Dream and Nightmare lab. Indeed, his research, and that of others over the years, shows hundreds of dreamers reporting they felt incredibly lifelike cuts, aches, and burns, as one 2011 study of more than 400 people in the International Journal of Dream Research reflects. So where does the sensation come from, and why?

Even within the comforts of your dream world, sensations of physical pain can exist and feel devastatingly real.

According to Professor Zadra, there are two sorts of dream pain: the real and the phantom, and both are pretty rare – encompassing maybe half a percentage of all people’s dreams. “Real” pain occurs when an external sensation from the waking world – like when your limbs fall asleep into that numb pins-and-needles effect – seep into our dreams.

In one fascinating study, Zadra and colleagues used blood pressure cuffs to restrict people’s blood flow during REM sleep, and individuals consequently reported feeling the sensation in their dreams – whether it was running through icy snow, dancing painfully, or wrestling with the cuff itself.

But what Zadra finds much more fascinating (and uncommon) is phantom pain: the kind your brain produces and plays out entirely within the confines of the dream, whether by cribbing off a memory of hurt you once felt, or something you maybe saw on “Game of Thrones”. “[People] will wake up from instances where they were being tortured, or they had a spear in their ribs, and describe it as horrendous or unbearable,” says Zadra. “But the pain sensation disappears the second they wake up.” That physical pain has no actual source in the real world, he says.

Unfortunately, the mechanisms behind how the brain creates that pain aren’t well known, given that the concept of pain, even in waking life, is still a big subject of debate. And according to Stanford psychiatry professor, Luis de Lecea, it’s “difficult” to experience pain in sleep, given our sensory pathways are mostly" disconnected" from cortical input from the real world. Zadra does suggest that the “neuromatrix” model — the idea that pain is a subjective construct of the mind — could explain how the brain creates hurt in dreams, too.

But what about dreams where horrendous things happen, but you feel nothing at all? What determines when you feel pain in a dream, or not?

It’s often the people who feel pain in their waking lives (burn victims, those with back pain, etc.) that are most likely to experience dream pain, since they have an existing memory of it.

Zadra recalls one patient who dreamt being hit by a baseball and feeling no pain. Another reported the same thing after they imagined slicing their skin. To this, he has some theories, one of which is that perhaps the brain only “produces” physical pain when you feel negative emotions in the dream such as anger or fear, since these strong primary emotions often co-occur with reported pain in studies. Another suggestion is that pain only occurs if you dream during the most intense phase of REM sleep — that long, deep cycle that occurs before you wake up. But with sleep research largely relying on reports from patients, even these theories are just theories, and require more exploration. 

Finally, there’s the question of what feeling pain in dreams says about us — whether it reveals some Freudian slip of ourselves, or not. Unfortunately, there isn’t much to dig at there. Studies show it’s often the people who feel pain in their waking lives (burn victims, people with back pain, etc.) that are most likely to experience dream pain, since they have an existing memory of it.

People still dream of pain they have never felt, however, as one Sleep and Hypnosis study, which tracked more than 6000 dreams of one patient over the course of 15 years, showed. And creating pain during our dreams may be the strongest indication of just how intense and realistic dreams can be.

It’s a testament to the mysterious wonders of the human brain that even virtual violence can be dreamt up. “If we feel that dreams are created from our brains, it’s absolutely fascinating that dream characters can scare us, get angry, seduce us, make us fall in love, and your brain is creating all this, and surprising itself,” says Zadra.

So, take it as both good and bad news: Those evil clowns and masked killers we see in nightmares will feel terrifyingly real, but when we wake up we feel relief — and no lingering pain. After all, it was just a dream.