How often would you say you struggle to stay or fall asleep? If it's more than three times per week (and has been going on for at least one month), then you might have one of the most common sleep disorders: insomnia.

Insomnia is often used to refer to any sort of difficulty sleeping, though official clinical diagnoses exist. Some of the diagnostic criteria include nonrestful sleep, daytime difficulties stemming from a lack of sleep, and difficulty sleeping despite opportunities to do so. (See US clinical diagnostic criteria).


Insomnia can be caused by a wide array of behaviors, events, and circumstances, such as dealing with the death of a loved one, napping too close to bedtime, or taking certain medications.

Many cases of insomnia are secondary, meaning the insomnia itself is a symptom of another condition, such as anxiety or sleep apnea. Nearly half of all people with chronic insomnia have a comorbid psychiatric condition.

The neurobiology of insomnia isn't fully understood, and several theories seek to explain the phenomenon, which appears to be at least partially influenced by genetics.

One proposes that insomnia may be a disorder of hypervigilance or hyperarousal experienced throughout the day—this sort of state occurs when a person attempts to be constantly aware of any threats, leaving them tense, anxious, and easily startled. Another suggests the disorder stems from an issue with the sleep-wake cycle controlled by one's circadian rhythm.

Risks for developing insomnia include gender and age (women and older adults have a higher chance of developing the disorder), working night or rotating shifts, and having comorbid medical or mental health disorders, including PTSD, anxiety, and depression.

Health Impacts

Acute, short-term sleep loss can trigger higher activity levels of dopamine, a hormone and neurotransmitter related to reward, memory, and motivation. A 2023 study found a sleepless night led mice to be less depressed and more aggressive than the rested control group.

But two nights without any sleep? People's decision-making abilities begin to suffer, leading to blunted reactions and failures to adapt to changing circumstances.

Sleeping less than seven hours per night is associated with increased pain perception and higher risks of diabetes, heart disease, depression, and death.

Sleeping less than six hours increases heart rate and decreases activity in the parasympathetic nervous system, which controls the body's ability to relax.

This "tired-but-wired" state can further impede a good night's sleep, beginning a deleterious cycle of sleep loss and harmful health effects.

Human behavior and cognitive performance are nearly drunken after four nights of five or less hours of sleep—common during parenthood, college, and professional training.

The brain might try to overcome the sleep gap by briefly offloading different regions, a phenomenon known as "local sleep" that may explain at least some of the cognitive issues that crop up when humans get sleepy.

Research shows that sleep deprivation also contributes to the gathering of misfolded proteins in and around neurons (such collections of misfolded proteins are believed to contribute to Alzheimer's).


There's no one-size-fits-all cure for insomnia, though interventions typically begin by improving sleep hygiene, encouraging people to adjust their sleep habits and presleep behaviors to better prioritize rest and relaxation.

Other common treatments include cognitive behavioral therapy and medication.

Some insomniacs find sleep by giving into the age-old bi- or polyphasic approach. This segmented approach to sleep is used across the animal kingdom and may have been humanity's go-to choice before the Industrial Revolution (and regular access to electric lights).

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The term "insomnia" is often used in popular culture to refer to general difficulty sleeping or staying asleep. In the US, insomnia transitions to a clinical disorder when symptoms—dissatisfying, nonrestful, and life-disrupting sleep—occur at least three nights per week for at least one month and cause "clinically significant" distress in important areas of functioning, such as school, work, or relationships.

Harvard University

What causes insomnia?

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Insomnia typically occurs in people dealing with life stressors and physical or mental health conditions, though the exact cause continues to elude researchers. A model proposed in the 1980s summarizes many of the theories for what causes insomnia, arguing that insomnia occurs due to predisposing, precipitating, and perpetuating factors, such as a family history of insomnia, reading with an eReader, or napping near bedtime.

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The biological process Shakespeare referred to as the chief nourisher of life's fleet is necessary for the body and mind to rest and repair from activities of daily life. As sleep evades the exhausted, sufferers also lose emotional stability, mental clarity, social connections, and more while simultaneously gaining waves of interrupted biological processes that can lead to disease and death.

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Growing evidence suggests genetics influence when, how long, and how well one sleeps, meaning insomnia may have a genetic component. While exact insomnia biomarkers have yet to be determined, some genes, including those related to psychiatric disorders, have been implicated. Sleep is also influenced by environmental and social factors, like staying up late to meet a deadline or Santa, complicating the search for insomnia's genetic underpinning.

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According to this illustrated journey into sleep, when one sleeps may be just as important as getting enough of it. "Molecular clocks" made of timekeeping proteins and genes help regulate the body and its processes, meaning the disruption of one cog will impact another. Those who live in sync with their circadian rhythms report less fatigue, clearer thoughts, greater medication benefits, and better long-term health outcomes.

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The body's sleep-wake cycle is one of its many circadian rhythms, which are behaviors or biological processes that exhibit 24-hour patterns. These rhythms are deeply impacted by light exposure, food availability, and much more, meaning where you live affects your sleep. Rural populations often exhibit earlier sleep patterns and less social jetlag—the mismatch between one's natural circadian rhythm and work or social demands—compared to urban populations.

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