Imagine regularly waking up exhausted, not because you didn’t sleep, but because you seemingly spent the entire night immersed in incessant dreams. For people who experience such “epic dreaming”, the effects can be severe, often impacting their work and day-to-day lives.

“These vivid experiences linger in my mind, drain my energy and create lasting fatigue,” said one such epic dreamer.

This woman, identified as 38-year-old Madame R, is one of four epic dreamers who have been assessed at two centres in France. Though scientific descriptions of epic dreams date back more than 20 years, the four detailed case studies support the idea that it should be recognised as a distinct sleep disorder, according to the researchers, who included Pierre Geoffroy at Paris Cité University.

During her assessment, Madame R said she has always experienced epic dreaming, but it worsened after the birth of her second child. The other case studies include Monsieur W., a 74-year-old man who said his intense, vivid dreams are “at times indistinguishable from reality”.

Then there’s Monsieur D., a 58-year-old man who reported four years of twice-weekly excessive dream activity, and Madame W., a 40-year-old woman who can’t remember a time without it. “It feels like my brain never stops at night,” she said.

Dreams can happen during any of the four stages of sleep, but the vivid, story-based nature of those reported by these individuals would suggest that they probably mostly occur during the rapid eye movement (REM) stage, says Geoffroy.

Excessive dreaming might suggest that someone is spending a disproportionate amount of time in the REM stage, but when three of the four individuals underwent polysomnography – an overnight test that measures brainwaves and eye movement – the results showed that they had typical, or even slightly shorter-than-average, durations of REM.

Overall, the polysomnography data was “largely unremarkable”, says Geoffroy. However, there were signs of greater REM density – more frequent and intense rapid eye movements – and more REM fragmentation — micro-arousals, which disrupt a continuous period of REM sleep. Frequent micro-awakenings may increase dream recall and create the impression of dreaming all night, says Geoffroy. Research supports the idea that our perceptions are powerful when it comes to sleep.

In addition, if someone’s brain repeatedly encodes dream material as vivid and absorbing, they may wake unrefreshed even when their sleep data looks acceptable, says Ivana Rosenzweig at King’s College London. “In other words, this may be less about whether the patient literally dreamt every second of the night and more about why the sleeping brain has failed to make dreaming feel contained, forgettable and separate from waking life.”

The researchers also investigated whether epic dreaming may be a symptom of poor mental health, which can cause disturbed sleep. All four of the individuals completed psychiatric assessments, with three of them showing signs of experiencing depression or anxiety. But treating the individuals for these conditions didn’t put a stop to their excessive dreaming, says Geoffrey, which he says supports the idea that epic dreaming is its own disorder. It also suggests that epic dreaming may be under-recognised if it is bundled with other sleep problems experienced by people with mental health conditions, says Geoffrey.

Rosenzweig says the paper “brings serious clinical attention to a phenomenon that many sleep clinicians will recognise but that has remained fairly poorly captured by our current diagnostic categories.” But more studies with larger groups of participants are needed before epic dreaming could be labelled as a distinct sleep disorder, she says.

Francesca Siclari at the Netherlands Institute for Neuroscience in Amsterdam also thinks that more research is needed. “One important challenge for the field will be determining whether excessive dreaming reflects a single mechanism and syndrome, or rather a symptom dimension that can emerge across different sleep or psychiatric conditions,” she says.

Future studies could also unpick why some epic dreamers find it difficult to distinguish between real and dreamed events, says Rosenzweig, which she and her colleagues have reported on. “In that sense, epic dreaming is not just an unusual sleep complaint, but may be a window onto a fundamental problem in neuroscience – how the brain decides what is real,” she says.