We have all been able to have ever a nightmare or a dream so real that it has left us with a very bad body when we wake up. Normally, we attribute this to stress, poor digestion or that movie we watched before going to sleep. However, neuroscience explores whether it is actually associated with a warning that the body gives us. because a disease is approaching that will generate physical symptoms.
It is already known. This phenomenon is known as ‘prodromal sleep‘, and although the idea may sound like science fiction or pseudoscience, a recent study published in 2025 has put on the table a neurobiological model that explains how and why this happens.
How it works. To understand prodromal dreams, we must look at the REM phase of sleep, which is precisely when the brain is not “off” and is precisely the moment in which dreams appear. But in addition to this, it is doing an intensive internal analysis, processing what is known as interoceptive signals, that is, the information that arrives about the state of our organs and tissues.
From this moment on, the McNamara model can be applied, which is based on the theory of “predictive coding” by neuroscientist Karl Friston. What we are looking for here is basically that our brain works like a prediction machinesince it constantly generates hypotheses about how our body should be when compared to a state of health.
What happens. Within these hypotheses, it may happen that, if there is a subtle imbalance in the body such as the beginning of an infection, the brain detects an “error” between what it expected to find (which is being healthy) and what is really happening, which is the beginning of an infection.
Since during REM sleep we do not have access to conscious logical thinking, the brain here turns to areas such as the amygdala, which manages threatening emotions, the insula that processes interoception, and the medial prefrontal cortex to translate the alert into a visual metaphor. Thus, a respiratory difficulty that we cannot detect, such as early pneumonia, could translate into a recurring dream in which we are drowning, or the prelude to a severe migraine could manifest itself as a dream in which we are chased. And what’s more, we can remember because it has been very marked.
The demonstration. The concept is not new, but already in 1967, researcher Kasatkin documented dozens of cases of patients who experienced distressing dreams just before suffering a heart attack. However, modern science has been able to go a little further by finding precisely the mechanism that justifies this type of dreams.
One of the most striking cases of investigation is in Parkinson’s diseasesince before the famous tremors appear, many patients develop sleep problems. In this case, those who suffer from a sleep behavior disorder do not have the usual muscle paralysis of the REM phase, which causes them to “act out” very aggressively in their dreams.
There are more cases. Other documented examples include patients with chronic migraineswhere it has been reported that up to 40% report nightmares prior to pain, or the curious reports from the first waves of COVID-19, where vivid dreams were the first “symptom” reported in several cohorts of patients.
Stop the ‘hype’. Logically, having a horrible nightmare tonight does not mean that we will have a major infection the next day. Here science sets different limits, such as that it is a theoretical model where most of the evidence is based on observational studies. This is why there is a lack of longitudinal studies that allow us to confirm this direct relationship.
But despite these limitations, the advances we are seeing with studies focused on polysomnography and advances in wearables and apps Sleep monitoring could, in the not too distant future, help us use our own nights as the most sophisticated early warning system in the world to anticipate certain diseases.
Images | Dmitry Ganin
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