Most of us, at one point or another, have probably been told to “sleep on it.” Taking the night to reflect on a pressing concern, we’re told, can help uneven emotions settle enabling us make more rational and careful decisions. Turns out, this phenomenon is more than just an old wive’s tale. A growing body of research suggests that sleep, or lack thereof, truly can influence emotions, mood, memory, decision-making, aggression, and more.
While asleep, your body and brain are doing much more than simply resting or powering down. Your body also clears out waste byproducts of waking activity, repairs tissues, and balances hormones. Because the processes taking place during sleep are so complex, there are many potential ways that both resting and not resting can affect brain chemistry and thereby impact emotional regulation, memory, mood, and other factors outlined below.
Emotional Response
When we are in control of our emotions we’re more likely to assess a situation and respond appropriately. Often parents will say that all their screaming grumpy child needs is a nap to recalibrate their emotional response. Science also supports this idea: One study looked at sleep’s effect on cognitive reappraisal, the ability to reframe and reduce the impact of an emotional event. After controlling for confounding factors, researchers found that poor sleep quality was associated with decreased ability to regulate negative emotions.
After a good night’s rest, subjective reactivity to emotional experiences was also reduced. Though the exact relationship between emotions and sleep remains a mystery, researchers suggest that reduced activity of the amygdala, the brain’s emotional center, during REM sleep may play a role. Previous research also suggests that sleep plays a protective role in emotional processing and attenuation.
Memory
We rely on our memories as a frame of reference for decision making and for interpreting events. Sleep could affect memory in several ways, including how we process and store new memories, and our ability to accurately retrieve old ones.
Sleep is hypothesized to play a crucial, active role in committing short-term memories of the day to long-term storage. It may also affect memory accuracy. One recent study found that being sleep deprived impaired people’s ability to accurately recall events, and actually made them more susceptible to false memories.
In other research, sleep deprivation and poor sleep quality were found to affect the emotional valence, or tone, of memories. People memorized and rated images on emotional valence, and then they were divided in groups indicating sleep deprivation, poor sleep, and good sleep. The following day, those who were sleep-deprived and poor sleepers were more likely to remember things in a more negative tone.
There’s also evidence that we are more likely to remember things that match our current mood. If you are happy, for example, pleasant memories are more forthcoming, whereas in times of sadness or anger, less pleasant memories emerge more easily.
Temperament
The mood we are in can color how we perceive things that happen to us, how we interact with others, as well as motivation to do things like exercise or work.
Related: A Bedtime Meditation to Prepare for Sleep
A three-week study of teenagers compared a week of baseline sleep, sleep-deprivation, and healthy sleep to determine impact on mood. During sleep deprivation, teens rated themselves as more anxious, angry, and confused, while parents also noted greater irritability and worse emotional regulation.
In another study, a group of researchers measured the effects of one night of sleep deprivation on subjective mood and stress. Sleep-deprived people reported higher levels of stress, anxiety and anger on low-stress tasks compared to well-rested people.
If our ability to regulate emotions and moods are affected by too little sleep, it stands to reason that we might be a little more on edge and prone to anger than usual when sleep-deprived.
A literature review looking at studies on sleep and aggression found connections between sleep deprivation and increased anger, expression of aggression, and short-temperedness. Exact causes are difficult to identify, but researchers suggest that this relationship may be a result of impaired prefrontal cortex functioning (responsible for control and regulation of emotions) and for some individuals, variations in neurotransmitter and adrenal systems.
Among couples, one study found that people reported more conflict on days following poor sleep in their normal lives. When studied in a laboratory setting, poor sleep resulted in reduced ability to accurately gauge partners’ emotions. Good sleep for both partners was associated with higher likelihood for conflict resolution.
Decision Making
A few different aspects of cognition are involved in making decisions, and while mood and memory play important roles, there’s even more going on.
According to one study, sleep deprived people are more likely to make unethical decisions at work. Researchers looked at nurses in a hospital setting and students in a lab setting, concluding that sleepier people were more likely to behave “deviantly”, including intentionally reducing productivity, being rude to customers, and demonstrating a higher temptation to steal.
They hypothesize this phenomenon is largely due to reduced capacity for self-control, and other research suggests depleted glucose stores may affect frontal lobe functioning required for complex thought and decision making, increasing unethical actions.
The Importance of a Good Night’s Sleep
Taken together, the research makes a strong case for getting a good night’s sleep on a regular basis, but particularly before reacting to emotional events or making difficult decisions. Emotions, moods, interpretation, memory, and our ability to analyze a situation may all suffer with a lack of sleep. On the other hand, getting a good night’s rest boosts your brain and helps balance your mental state in support of wiser decisions and healthier relationships.
Related: How Poor Sleep Impacts Mental Health in Students
Following good sleep hygiene habits on a daily basis is a wise move for everyone. Sleeping and waking on a regular schedule, getting at least seven hours, getting regular exercise and good nutrition, and taking time to de-stress all help contribute to better rest.
If you find yourself facing an emotionally charged situation, sleep may be even more important. Clear your mind before bed with meditation or yoga, and then take the night to sleep on a tough decision and temper your thoughts. If it’s midday, a quick afternoon nap may also be a useful tool for balancing your mind.
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