Why we dream is somewhat of a mystery, however, scientists may have edged one step closer to cracking it.
With our loved ones, home and workplace often featuring in our dreams, the nighttime hallucinations are known to draw on people's memories.
A team from Furman University in South Carolina wondered whether these past "fragments" may be combined into "imagined simulations of events" that prepare us for the future while we sleep.
To put their theory to the test, the scientists analysed 48 students who spent a night in a laboratory. With many people not remembering their dreams the next day, the students were woken up to 13 times, reporting on any nighttime hallucinations they had experienced.
The next morning, the students explained whether their dreams related to a "source" in their life.
More than half (53%) of the dreams could be traced to a past memory, while a quarter (25%) "were related to specific impending future events". The scientists concluded dreams "not only reflect past memory, but also anticipate probable future events".
Whether it's envisioning an ex with a new partner or not landing that promotion, dreams may help to prepare people for what could be to come.
"Humans have struggled to understand the meaning of dreams for millennia," said lead author Dr Erin Wamsley.
"We present new evidence that dreams reflect a memory-processing function.
"Although it has long been known that dreams incorporate fragments of past experience, our data suggest dreams also anticipate probable future events."
After the students spent a night in the laboratory, the scientists found more than third (37%) of the dreams "with a future event source" were "related to one or more specific past memories".
"Future-oriented dreams" became more common later in the night.
Based on their results, published in the journal Sleep, the scientists believe dreams utilise "fragments of past experience to construct novel scenarios anticipating future events".
"While these dreams rarely depict future events realistically, the activation and recombination of future-relevant memory fragments may nonetheless serve a function", they wrote.
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