Insomnia: Symptoms, Causes, and What Really Helps | sleep²

You lie awake even though you're tired. Thoughts are racing, your eyes wander to the clock, and the next day you're out of energy. When this repeats over weeks, it has a name: insomnia. It is the most common sleep disorder overall and affects around 10% of adults in chronic form. Nevertheless, it is often dismissed as a mood issue or addressed with sleeping pills, even though international guidelines have recommended a different approach for years.

This guide explains what insomnia is, how to recognize it, what sustains it, and what studies have shown to actually help. At the end, you'll find a self-check with four questions and guidance on when medical clarification is advisable.

What is Insomnia? Definition and Criteria

Insomnia refers to difficulty falling or staying asleep that occurs despite adequate opportunity to sleep and noticeably affects the day: fatigue, concentration problems, irritability, or performance issues are part of the picture. Those who sleep poorly but feel fine during the day do not meet the criteria. The International Classification of Sleep Disorders (ICSD-3) defines chronic insomnia by four criteria: Problems occur on at least three nights per week, persist for at least three months, occur despite adequate opportunity to sleep, and lead to daytime impairment. If symptoms last less than three months, it is called acute insomnia, such as after a stressful event. It often resolves on its own but can become chronic.

How Common is Insomnia?

About 10% of adults suffer from chronic insomnia, and another 30% report occasional symptoms. An epidemiological review (Morin & Jarrin, 2015) estimates 10–15% with clinically relevant chronic insomnia and 30–35% with symptoms. Women are about 1.5 times more likely to be affected than men. As we age, sleep becomes more prone to disturbances: the proportion of deep sleep decreases and often falls below 15% from around age 50. Our article on the four sleep phases explains the role of each stage. In the U.S. alone, costs are estimated at over $100 billion per year (Wickwire et al., 2016).

What Are the Symptoms of Insomnia? The Four Manifestations

Not all insomnia is the same. In practice, four phenotypes are distinguished, which can occur individually or in combination. Difficulty falling asleep: You regularly take a long time to fall asleep. Difficulty staying asleep: You wake up multiple times during the night and lie awake for a long time afterwards. Early awakening: You wake up significantly earlier than planned and can't fall back asleep. Non-restorative sleep: The sleep duration seems adequate, yet you feel exhausted in the morning. Our article on quality over quantity in sleep explains why this can happen.

Causes: Why Insomnia Sustains Itself

Insomnia rarely arises from a single cause. Spielman's 3-P model describes three interacting factors. Predisposing factors like increased stress reactivity make some people more susceptible. Triggering factors such as a work crisis, illness, or breakup disrupt sleep. Crucial are the sustaining factors: behaviors and thoughts that should help but worsen sleep in the long run, like staying in bed longer, napping during the day, or worrying about the next night.

This creates a vicious cycle: poor sleep leads to worry, worry leads to tension, and tension prevents sleep. Sleep research refers to hyperarousal, a state of increased physical and mental activation that extends into the night. Insomnia is also closely linked to mental health: it doubles to triples the risk of developing depression (meta-analysis by Baglioni et al., 2011, Odds Ratio around 2.6). More on this in our article Why Poor Sleep Can Cause Depression.

Differentiation: Insomnia or Something Else?

Not every poor sleep is insomnia. The most important differentiation is obstructive sleep apnea (OSA): Breathing repeatedly stops during sleep, and the body responds with brief awakenings, often unnoticed. Typical signs include loud snoring, observed breathing pauses, morning headaches, and pronounced daytime sleepiness despite seemingly adequate sleep duration. Severity is determined by the apnea-hypopnea index (AHI): 5–15 events per hour are mild, 15–30 are moderate, over 30 are severe. Untreated OSA is associated with hypertension, cardiovascular diseases, and stroke; hundreds of millions of people worldwide are affected, many undiagnosed. Restless legs syndrome, rhythm disorders, pain, or medications can also cause sleep problems. In such cases, medical evaluation is necessary before starting insomnia therapy.

What Helps with Insomnia? CBT-I as the First-Line Therapy

All major international guidelines, from the American Academy of Sleep Medicine (AASM) to the European Sleep Research Society (ESRS) and the German Society for Sleep Research and Sleep Medicine (DGSM) to the British NHS, recommend cognitive behavioral therapy for insomnia (CBT-I) as the first-line therapy, not sleeping pills. Insomnia is not a lifestyle problem. It is an independent, well-treatable sleep disorder.

CBT-I is a structured program consisting of six components. Psychoeducation explains how sleep works and why the vicious cycle occurs. Sleep hygiene eliminates disruptors like evening caffeine. Stimulus control re-associates the bed with sleep: go to bed only when tired, get up if awake for a long time, fixed wake-up time. Sleep restriction temporarily shortens time in bed to actual sleep time to increase sleep pressure. Cognitive techniques address thoughts that fuel wakefulness. Relaxation techniques like progressive muscle relaxation lower activation levels. Sleeping pills can be useful in acute phases, short-term, and medically supervised, usually not longer than four weeks according to European guidelines (Riemann et al., 2023); they do not change sustaining habits and thoughts.

The problem is implementation: only a fraction of people with insomnia receive CBT-I. Digital programs deliver the components in a structured way through an app and are now part of care: In Germany, digital health applications can be prescribed by doctors since 2020, and health insurers include digital sleep programs in their offerings. The goal is blended care, where doctor, app, and AI-supported guidance work together. The intensive program from sleep² follows this approach: CBT-I-based, CE-certified as a medical device in the EU, and examined in three studies by the University of Salzburg. In two randomized controlled trials with a six-week program version (Hinterberger et al., 2023; Eigl et al., 2023), insomnia severity and subjective sleep quality (ISI and PSQI questionnaires) improved significantly more than in control groups; in polysomnography, nighttime wake time in the training group decreased from about 59 to 43 minutes, and sleep efficiency increased from 86 to 89% (Eigl et al., 2023). In a field study with 88 people and an eight-week version (Hinterberger et al., 2025), the proportion with insomnia symptoms decreased from 92 to 67%, and in the sleep diary, sleep onset time and nighttime wake time each shortened by about a quarter, while objective sensor data remained largely stable. Today, the program lasts eight weeks and remains open for twelve weeks to realistically complete it in everyday life.

Sleep Diary and Objective Measurement: Two Perspectives on the Same Night

The foundation of any CBT-I is the sleep diary: bedtime, estimated sleep onset time, wake phases, wake-up time, daytime well-being. It represents the subjective side on which the diagnosis is based. An objective measurement complements this view, and the two rarely match: those who lie awake for long periods often experience the night as much shorter than it was. This discrepancy is therapeutically valuable because it helps to test catastrophic thoughts against reality. Many consumer trackers underestimate short wake phases by more than 50% and often identify sleep stages only near the chance level. In a comparison study by the University of Salzburg against polysomnography (PSG), the gold standard of sleep measurement, sleep² with the Polar Verity Sense on the upper arm achieved a sleep stage accuracy of 83.7% and a mean deviation of total sleep time of about 6 minutes (Topalidis et al., 2025, https://osf.io/preprints/psyarxiv/27wun_v1). More on this in our article on sleep trackers for sleep analysis.

Self-Check: Do I Have Insomnia?

The four questions are based on the ICSD-3 criteria:

1. Do I have trouble falling or staying asleep on at least three nights per week, or do I wake up significantly too early?
2. Has this been going on for more than three months?
3. Does it happen even though I give myself enough time and a suitable environment for sleeping?
4. Do I feel affected during the day, such as tired, unfocused, or irritable?

If you answer all four questions with yes, the criteria suggest chronic insomnia. A first step is the basics from our article Improving Sleep; for persistent symptoms, structured CBT-I is the next step. Medical clarification is advisable if snoring or breathing pauses are observed, if physical symptoms, severe mood swings, or medications are involved, or if you regularly take sleeping pills. The first point of contact is the general practice.

Frequently Asked Questions About Insomnia

What is Insomnia?

Insomnia is a sleep disorder where falling or staying asleep fails despite adequate opportunity, and the day suffers as a result. It is chronic according to ICSD-3 from three nights per week over more than three months.

How Many People Have Insomnia?

About 10% of adults suffer from chronic insomnia, and another 30% experience occasional symptoms (Morin & Jarrin, 2015: 10–15% or 30–35%). Women are about 1.5 times more likely to be affected than men.

Is Insomnia Curable?

Insomnia is well-treatable. Cognitive behavioral therapy for insomnia (CBT-I) is the first-line therapy according to guidelines. In two randomized controlled studies on the CBT-I-based program from sleep² (Hinterberger et al., 2023; Eigl et al., 2023), insomnia severity and sleep quality (questionnaires) improved significantly, and in polysomnography, nighttime wake time decreased from about 59 to 43 minutes.

What Therapy Helps with Insomnia?

CBT-I, recommended by AASM, ESRS, DGSM, and NHS, with six components: psychoeducation, sleep hygiene, stimulus control, sleep restriction, cognitive techniques, and relaxation methods. Sleeping pills help only short-term, medically supervised, and according to guidelines, usually not longer than four weeks.

What is the Difference Between Insomnia and Sleep Apnea?

In insomnia, the problem is falling or staying asleep with increased tension; breathing is normal. In sleep apnea, breathing repeatedly stops during sleep. Severity is determined by the apnea-hypopnea index: 5–15 events per hour mild, 15–30 moderate, over 30 severe.

When Should I See a Doctor for Sleep Problems?

If sleep problems persist for more than three months, if snoring or breathing pauses are observed, if physical symptoms, mood swings, or medications play a role, or if sleeping pills are regularly taken. The first point of contact is the general practice.

If you want to understand your sleep objectively and improve it in a structured way: sleep² is available in the App Store and on Google Play, more about the intensive program at www.sleep2.com.