For decades, the science of sleep assumed that deeper rest meant a quieter brain — slow waves, minimal activity, little awareness. Dreaming, by contrast, has long been associated with a more active brain state, one that resembles wakefulness. This seemed to create a contradiction: if dreaming meant brain activity, how could it also feel like deep sleep?
A team of researchers at the IMT School for Advanced Studies Lucca, in Lucca, Italy, has now offered a compelling answer. Their study, published in PLOS Biology, analysed 196 overnight sleep recordings from 44 healthy adults. Participants were woken repeatedly during non-REM sleep and asked both to describe their mental experiences and to rate how deeply they felt they had been sleeping. Across more than 1,000 individual awakenings, a consistent pattern emerged: people reported the deepest, most restorative sleep not only after periods of no mental activity, but also after vivid, immersive dreams. The more absorbing the dream, the deeper the sleep felt.
The researchers also noticed something unexpected as the night progressed. Biological markers of the body's need for sleep naturally declined through the hours — yet participants reported feeling that their sleep was becoming deeper, not shallower. This shift closely tracked an increase in dream immersiveness. The team described dreams as acting as "guardians of sleep": rather than pulling the mind toward wakefulness, an engaging inner dream world appears to insulate the sleeper from external disturbances and maintain the sensation of deep rest.
Professor Giulio Bernardi, neuroscientist and senior author of the study, noted that the quality of the dream experience — particularly how immersive it felt — appears to be the crucial factor. The findings could help explain why some people feel poorly rested despite showing normal sleep readings in clinical tests.