Perhaps you go to bed early and sleep as usual, but you wake up feeling like you’ve run a marathon. Your mind feels foggy, your body heavy, and when you get up, it seems like all your energy has gotten trapped somewhere under the sheets. Then you remember that you spent the night dreaming. A lot. Maybe you had several intense, strange, or emotionally draining dreams. And you conclude that you’re tired because you dreamed too much.
It’s a widespread belief. Many people are convinced that nights when they dream more are less restorative. However, neuroscience tells a different story.
We dream much more than we believe
Although some people claim they never dream and others say they dream very little, the truth is that we all dream every night. Several times. Most dreams occur during REM (Rapid Eye Movement) sleep, a stage characterized by intense brain activity.
According to sleep physiology, this phase occupies approximately 25% of the total time we spend sleeping and has several cycles throughout the night, the first of which begins between 70 and 90 minutes after we fall asleep. Each night we go through between 4 and 6 REM sleep cycles, although each one lengthens as morning approaches.
The curious thing is that we don’t usually remember most of those dreams. Our brain generates them and, just as quickly, leaves them behind without them ever reaching our conscious awareness. So why are some dreams memorable?
The answer has less to do with the number of dreams and more to do with when we wake up. When we wake up during or immediately after REM sleep, we’re more likely to remember what we were dreaming. And the more emotionally intense the dream was, the more likely it is to be etched in our memory.
In fact, people who acknowledge dreaming a lot and remember those dream contents more clearly also tend to have lighter and more fragmented sleep, simply because they wake up several times throughout the night.
Researcher Tore Nielsen developed a theory according to which remembering a dream requires a brief brain activation or awakening near the end of the REM episode. His work supports the idea that recalling dream content is largely a consequence of more fragmented sleep.
What happens in the brain when we dream?
For a long time, it was thought that when we slept, the brain rested. Today we know that this isn’t entirely true. While we dream, especially during REM sleep, our brain remains surprisingly active. In fact, some regions show activity levels similar to those of the waking state.
Areas related to emotions, such as the amygdala and hippocampus, are intensely active. The amygdala is involved in emotional processing, while the hippocampus plays a key role in consolidating memories. In contrast, activity in the prefrontal cortex (the region responsible for logical reasoning, planning, and executive control) is significantly reduced.
This explains why dreams are often so strange and illogical. Emotions are running high, but the part of the brain that would normally question reason is less active. That’s why, in a dream, we can talk to a ghost, arrive late to an exam 20 years after finishing our studies, or find an elephant in our kitchen without it seeming odd.
Does dreaming consume energy?
At first glance, it seems reasonable to think that such an active brain must expend a huge amount of energy while dreaming, which could explain morning fatigue. However, neuroimaging studies suggest that this explanation is insufficient.
Although the brain consumes energy during REM sleep, that energy expenditure alone is not responsible for the feeling of exhaustion some people experience upon waking. In fact, if dreaming were inherently exhausting, we would all wake up tired every morning.
Science points to another culprit: nighttime awakenings.
The most important clue is that to remember a dream, we usually have to have woken up, even if only for a few seconds. Many of these awakenings are so brief that they don’t even reach conscious awareness. We don’t remember opening our eyes or changing position, but the brain has registered the interruption.
And that’s the problem. Sleep is made up of different phases. Some are lighter and others are deeper. Deep sleep is particularly important because various restorative processes occur during this cycle.
Among other things, our brain uses these phases to eliminate waste products from its daytime metabolism, reorganize information, and promote physical and cognitive recovery. One of these substances is adenosine , which accumulates in the brain throughout the day and eventually slows down brain activity and sends signals of fatigue.
When we have fragmented sleep, the time available for the brain to perform its functions decreases. In other words, you might not be tired because you dreamed a lot, but rather you remember those dreams precisely because you woke up several times. That is, the dreams aren’t the culprit, but simply a sign of those nighttime awakenings. They don’t cause the tiredness; rather, they act as evidence of what’s happening in our brain.
We’re not tired because we dreamed. We remember dreaming because our brain didn’t sleep as deeply as it needed to and couldn’t fully regenerate. That’s why we feel exhausted the next day. And that small difference completely changes the story we tell ourselves every morning when we open our eyes.
References:
Dal Sacco, D. (2022) Dream recall frequency and psychosomatics. Acta Biomedica: 93(2).
Nielsen, T. A. (2000) A review of mentation in REM and NREM sleep: «Covert REM sleep» as a possible reconciliation of two opposing models. Behavioral and Brain Sciences; 23(6): 851-866.
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