What Is Insomnia? The Features, Symptoms, and Causes

When Trouble Falling or Staying Asleep is a Disorder

A woman lies awake wondering, 'What is insomnia?'
A woman lies awake wondering, 'What is insomnia?'. Getty Images

Though it is the most common of the various sleep disorders, one may wonder: What is insomnia? How is insomnia defined and diagnosed? When struggling to sleep, it may be helpful to understand what insomnia is, how often it occurs, the potential causes, and its classic clinical features and symptoms.

What Is Insomnia?

Insomnia is characterized by an inability to obtain a sufficient amount of sleep to feel rested.

It can be due to either difficulty falling or staying asleep. It may also result in waking earlier than desired. The sleep is often reported to be of chronically poor quality, light and unrefreshing. In children, there may be resistance to going to bed or difficulty initiating sleep without a parent or caregiver being present.

The degree of sleep disturbance may vary, but insomnia typically involves taking 30 or more minutes to fall asleep or a total sleep time that is less than six hours on average. People with insomnia suffer from daytime consequences to these difficulties.

Chronic insomnia is defined to occur at least 3 nights per week for at least 3 months. It may last for years or even decades. Short-term insomnia (or acute insomnia) lasts less than 3 months with an unspecified frequency.

There are a number of subtypes of insomnia that help to differentiate the potential causes and may help to optimize the selection of treatments.

These subtypes include:

  • Psychophysiological insomnia: heightened arousal with excessive worry and focus on sleep.
  • Idiopathic insomnia: longstanding and genetically based, often beginning in infancy or childhood.
  • Paradoxical insomnia: sleep state misperception resulting in mistaken belief that sleep has not occurred.
  • Inadequate sleep hygiene: habits that disturb sleep including naps, caffeine intake, a variable sleep schedule, and using the bedroom for non-sleep activities.
  • Behavioral insomnia of childhood: usually either sleep-onset type in infants or limit-setting type in toddlers.
  • Insomnia due to a mental disorder: most often anxiety or depression.
  • Insomnia due to a medical condition: most often chronic pain or sleep apnea.
  • Insomnia due to drug or substance: may be due to intoxication or withdrawal from over-the-counter, prescription, or illicit substances.

In order for insomnia to be present, the above difficulties must occur despite adequate opportunity for sleep, so that it is not simply due to sleep deprivation. In addition, it must not be secondary to a poor sleep environment with excessive noise, light, or other disruptions.

Insomnia is diagnosed based on a careful history alone. In some cases, a sleep log or sleep-wake actigraphy may provide corroborative evidence. It is not usually necessary to have a sleep study unless another sleep disorder is believed to be responsible for the condition.

How Common Is Insomnia?

Insomnia is the most commonly encountered sleep disorder. Just how frequently it occurs depends on the study, the definition used, and whether one is assessing chronic versus intermittent or acute insomnia. In one study, 35% of adults reported insomnia of any type during the previous year. Approximately 10% of people have chronic insomnia that affects their daytime functioning, according to a review of 50 studies.

In addition, insomnia more commonly occurs as we get older. Women are more likely to report insomnia symptoms, in particular within the setting of sleep apnea that occurs beyond menopause. Insomnia also seems to be more common among those who are unemployed, single (from any cause), or of low socioeconomic status.

Symptoms of Insomnia

People who suffer from insomnia may experience numerous daytime symptoms, including:

  • Fatigue or daytime sleepiness
  • Poor attention or concentration
  • Impaired performance resulting in problems with work or social life and increased risk for errors or accidents
  • Reduced energy or motivation
  • Behavioral problems (i.e., hyperactivity, impulsiveness, aggression)
  • Mood problems, including anxiety or depression or irritability
  • Increased suicide risk
  • Headache and chronic pain complaints

Causes of Insomnia

Insomnia may be due to a number of possible causes. People with insomnia may have a predisposition towards developing the condition. This may be based in genetics, as insomnia often runs in families. It may occur due to an underlying circadian rhythm disorder. Those with insomnia are also found to have increased brain metabolism. As a result, they are more awake both during the day and at night. It may be associated with other disorders, including anxiety or depression and sleep conditions such as sleep apnea and restless legs syndrome. Chronic pain or nocturia (getting up during the night to urinate) may also disturb sleep.

Short-term insomnia is often triggered by specific precipitating factors. These may be environmental, psychological, or social. Factors that may potentially contribute to developing insomnia include travel, noise, light, or temperature. Stress from a lost job, financial problems, a divorce, or the death of a close friend or family member may contribute. Work or family responsibilities (including caring for infants) can also disturb sleep.

Chronic insomnia is often due to perpetuating factors. The relationship with sleep can change: suddenly it's stressful to try to sleep and the difficulties provoke anxiety or frustration that worsen it. The behavior of sleep can change as well. People with insomnia may go to bed earlier, stay in bed awake longer, and even try to nap during the day to make up for lost sleep. These actions may undermine sleep quality by extending the time in bed beyond what is needed to feel rested. Untreated coexisting sleep disorders frequently perpetuate insomnia.

As with any medical condition, it is important to rule out other potential causes of insomnia. In individuals with symptoms suggestive of insomnia, it is necessary to assess whether other medical or psychiatric problems, medications, or substance use may be contributing to the condition. For anyone who simply is not getting enough sleep by choice, insomnia would not be the correct diagnosis.

Insomnia is a common condition that should be properly identified so that efforts can be made to provide adequate treatment and relief from a disorder that can lead to significant impairment of one’s life. Fortunately, there are effective options, from the temporary use of sleeping pills to cognitive behavioral therapy for insomnia (CBTI). If you are struggling, speak with your doctor about the best therapy to resolve your condition.


American Academy of Sleep Medicine. International classification of sleep disorders, 3rd ed. Darien, IL: American Academy of Sleep Medicine, 2014.

Mellinger, GD et al. "Insomnia and its treatment: Prevalence and correlates." Arch Gen Psychiatry 1985; 42:225.

Ohayon, MM. "Epidemiology of insomnia: what we know and what we still need to learn." Sleep Med Rev 2002; 6:97.

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