Scientists have reported a two- to fourfold increase in the prevalence of dream-enactment disorder – whereby people physically act out their dreams – during the pandemic, with those who have been infected with Covid the most likely to experience it.

Given that the phenomenon can be an early indicator of Parkinson’s disease, it is possible the virus has triggered brain changes that could increase people’s risk of developing the condition. The researchers, however, stressed that it could also be the result of pandemic-induced stress and that further research was needed to explore the link.

Our muscles are usually paralysed during REM sleep, when most dreaming occurs, meaning our bodies remain quiet and still. In people with a rare condition called REM sleep behaviour disorder (RBD), however, this temporary paralysis doesn’t occur, leading them to physically act out their dreams. “They may punch or flail their arms in the air, make running movements, or even jump out of bed, sometimes resulting in injuries to themselves or their partner,” said Prof Yaping Liu at the Chinese University of Hong Kong, who led the research.

The condition affects 2-3% of adults over the age of 60 across the developed world, and in some cases can be a precursor to the development of Parkinson’s disease.

Liu and his colleagues became interested in whether the prevalence of dream-enactment disorder had increased during the pandemic after reading several scientific reports of people developing Parkinson’s-like symptoms shortly after becoming infected with Covid.

They examined data from the international Covid sleep study, an online survey of 26,539 people from 15 countries. Among the questions, it asked the participants if they had been told, or suspected themselves of acting out their dreams while they slept.

“We found that the prevalence of dream-enactment behaviour was two to four times higher than previous studies that have been conducted in the general population during non-pandemic times,” said Liu. “Moreover, in those subjects who reported a Covid-19 diagnosis, it was two or three times higher, compared with subjects without infection.”

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Their study, published in the Journal of Sleep Research, found that 8% of people with a Covid diagnosis regularly experienced the phenomenon, against 3% of those who had never been infected. It was not able, however, to determine whether these behaviours occurred only during the infection itself or continued after people had recovered from Covid.

Prof Adam Zeman, an expert in sleep disorders at the University of Exeter, said the finding was intriguing, but raised more questions than it answers. “The overall rate of dream-enactment detected in the study was extremely high, suggesting that a variety of different sleep behaviours may have led respondents to report it.

“If Covid-19 truly raises the rate of dream-enactment, there may be a variety of explanations, from anxiety to obstructive sleep apnoea,” he said, referring to a condition in which a person’s breathing stops and starts during sleep.

The possibility of a link between Covid-19 infection and a form of Parkinson’s disease would require further research using more objective ways of diagnosing it, he added.

Prof Michele Hu at the University of Oxford, who is studying the links between Parkinson’s disease and sleep, said the definitive way of diagnosing RBD would be overnight sleep study, which is usually conducted in hospital. Liu’s study, however, was important because it raised a potential link between Covid-19 infection and RBD for the first time, she said.

Liu agreed that more research was needed: “Dream-enactment behaviours can also occur as a result of other sleep disorders such as sleep apnoea, and have also been reported by people with post-traumatic stress disorder, or who are experiencing nightmares,” he said. “They may be intermittent and fade away if other problems, such as nightmares, PTSD, stress, and negative emotions are improved.”

In the meantime, he said people should be aware of the possibility of becoming injured, or injuring their partner if they are acting out their dreams, and if the behaviours persist and become frequent they should seek medical advice.

The Sleep Foundation recommends removing sharp objects, clutter and furniture from around the bed, and if the individual shares a bed with their partner, considering sleeping in separate beds while the behaviour continues.