New research is challenging long-held assumptions about what defines a good night’s sleep, with scientists finding that vivid, immersive dreams may play a key role in how deeply people feel they have rested.
The study, conducted by researchers at IMT School for Advanced Studies Lucca and published in PLOS Biology, suggests that sleep is not simply about how long or how quietly the brain rests. Instead, the nature of mental experiences during sleep may significantly shape how restorative it feels.
For decades, deep sleep has been associated with a largely inactive brain, characterised by slow waves and minimal mental activity. Dreaming, on the other hand, has typically been linked to rapid eye movement (REM) sleep, a stage where brain activity resembles wakefulness. The new findings indicate that this distinction may not fully capture how people experience sleep.
Researchers analysed 196 overnight sleep recordings from 44 healthy adults using high-density electroencephalography (EEG) to track brain activity. Participants were awakened multiple times during non-REM sleep and asked to describe what they had been experiencing and how deeply they felt they had been sleeping.
Across more than 1,000 awakenings, the results showed that people often reported the deepest sleep not only when they had no conscious awareness, but also after experiencing vivid and immersive dreams. By contrast, fragmented or fleeting thoughts were linked to a lighter perception of sleep.
Giulio Bernardi, the study’s senior author, said the findings highlight an important distinction in how mental activity during sleep is perceived. He explained that not all brain activity feels the same to the sleeper, and that the intensity and immersion of dreams appear to influence whether sleep is experienced as deep or shallow.
The study also found an unexpected pattern over the course of the night. As sleep progressed, participants reported feeling that their sleep was becoming deeper, even though biological indicators suggested the body was becoming more rested and sleep pressure was decreasing. Researchers observed that this shift coincided with an increase in the vividness of dreams.
Scientists say this could help explain why some people feel they have slept poorly despite meeting standard measures of sleep quality, such as duration or sleep stages. If dream experiences shape the perception of rest, disruptions in dreaming could affect how refreshed a person feels upon waking.
The findings may influence how sleep quality is assessed in the future. Rather than relying solely on objective measures like brain waves or total sleep time, researchers suggest that subjective experiences, including dream intensity, could become an important factor.
Experts say the research opens the door to new approaches in sleep therapy, where improving the nature of dream experiences might help enhance overall sleep quality and well-being.