When her daughter is in kindergarten, Rebecca Spencer has experienced something that many parents and carers know: the power of nap.
Without a nap, her daughter was dizzy, grumpy, or both at the same time.
Spencer, a neuroscience specialist at the University of Massachusetts Amherst, in the US, wanted to know what was behind this anecdotal experience.
"Many people realize that a child without a nap is emotionally deregulated," he explains. "This made us ask ourselves the question:" Do you really help us to process the emotions? "
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Research has already shown that sleep generally helps us to understand emotions. Indeed, it plays a key role in encoding information derived from the day's experiences, so it is essential to keep memories.
And emotional memories are unique because of the way they activate the amygdala body: the emotional core of the brain.
"Activating the body of the amygdala is what lets you memorize your wedding day and the funeral of your parents more than any other business day," says Spencer.
The amygdala body designates these memories as meaningful so that during sleep they are treated for longer and repeated more than other trivial memories.
The result is that emotionally important memories are easier to recover in the future.
But by influencing the way memories are being processed, the dream can change the power they have.
"Sleep is especially effective when it comes to transforming emotional memory," says Elaine Bollinger, a specialist in emotion and sleep at the University of Tübingen, Germany.
In a recent study, Bollinger and colleagues showed negative and neutral images of children between the ages of 8 and 11. Children showed their emotional response by choosing simple human drawings.
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Later some of the children slept and others did not. Researchers control their brain physiology through the adjacent room electrodes.
The next morning the children saw the same images as some new ones. And compared to the children who stayed awake, the children who slept better controlled their emotional responses.
This study suggests that sleep helps crystallize emotional information and control how we feel. And this effect is happening quickly.
"A great deal of current research shows that one night's sleep is already useful," says Bollinger. "This is useful for memory processing and is also important for emotional regulation at all."
But not all dreams are the same.
Types of sleep
The rapid eye movement (REM) is accompanied by emotional memories and the larger REM sleep makes people better appreciate the intentions of others and memorize emotional stories.
One theory points to the absence of the stress hormone noradrenaline during REM sleep. Temporarily released from this hormone, the brain can process memories without stress.
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Simon Durant, Head of the Dream and Knowledge Lab at the University of Lincoln, England, highlights another aspect.
The prefrontal cortex is the most developed part of the brain: there is where Durant says: "the human impulse to keep calm and not react immediately to things."
During awakening, this is the part that keeps the body of the amygdala under control and therefore the emotions. During sleep, this relationship is reduced.
"In a sense, during REM sleep, emotion is raging."
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But Spencer believes that non-REM sleep also plays an important role. Sleeping Wave Sleep (SWS) is the first sleep phase that consolidates memories and is particularly effective in processing neutral memories.
Spencer's studies show that the amount of SWS activity during sleep has an impact on the way emotional memories are transformed.
Gaps consist mainly of non-REM sleep. And a recent article collected by Spencer seems to be the first to show that not only the night sleep contributes to the processing of emotional memory in children.
Without baking, children showed a bias towards emotion. With a nap they react in the same way as neutral stimuli and emotional stimuli.
In short, he assures that "if they do not remember, children become hypersensitive to emotional stimuli," because they have not consolidated the emotional luggage of that day.
Spencer believes that NGOs contribute to emotional treatment in adults, albeit not to the same extent. An adult has a more mature hippocampus and hence more ability to preserve memories. Do not sleep does not hurt them so much.
But this is only one moment. Spencer's aging studies suggest that "we need to consolidate memories more often when we get older."
Interestingly, older people show deviation to positive memories while young people tend to be negative.
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This may be due to the fact that children and adolescents focus on negative experiences because they contain key information that needs to be learned: from the dangers of fire to the risks of taking a drink from a stranger.
But towards the end of life, people give priority to the positive one. They also have less REM sleep, a type of sleep that will most likely save negative memories, especially in people with depression.
Sleep researchers also analyze the potential of some aspects of sleep for the treatment of post-traumatic stress disorder (PTSD).
One study shows that sleep within 24 hours after a traumatic experience makes these memories less disturbing in later days. For people with anxiety, sleep therapy can help them remember that they have removed their fears.
On the contrary, wake-up therapy – in which people are deliberately devoid of sleep – spreads as a method of treating depression.
Insomnia can in some cases have a protective effect. Spencer notes that after the trauma "the natural biological response under these conditions is to have insomnia."
Thus, sometimes it may be good that the lack of REM sleep impacts the ability of the brain to consolidate emotional memories.
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"There is evidence that people with longer REM sleep tend to be more depressed," said Durrant. The expert believes this is because a subgroup of people with depression once again consolidates negative memories during REM sleep.
"I do not think I will see how this problem is resolved," he says about all potential clinical applications of sleep and wake therapy.
But it is obvious that some types of decision-making are improving after sleep, partly because of the way the dream regulates all this rotating feeling.
Bollinger explains clearly: in general, "sleep helps you feel better".
After all, the best recipe for a broken heart or cloud can be a nap.
Read BBC Future's original English story.