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

You lie awake even though you're tired. Thoughts race, 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 and affects about 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 another approach for years.

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

What is Insomnia? Definition and Criteria

Insomnia refers to difficulty falling or staying asleep despite having enough opportunity to sleep, noticeably affecting the day: fatigue, concentration problems, irritability, or reduced performance 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 at least three nights per week, persist for at least three months, arise despite adequate opportunity to sleep, and lead to daytime impairment. If symptoms last less than three months, it's called acute insomnia, often 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 symptoms at least occasionally. An epidemiological review (Morin & Jarrin, 2015) reports 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. With 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 stages explains the role of each stage. In the USA alone, costs are estimated at over 100 billion USD per year (Wickwire et al., 2016).

What Insomnia Symptoms Are There? 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 at night and lie awake for longer periods. Early awakening: You wake up significantly earlier than planned and don't fall back asleep. Non-restorative sleep: The sleep duration seems sufficient, 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. The 3-P model by Spielman describes three interacting factors. Predisposing factors, such as increased stress reactivity, make some people more susceptible. Precipitating factors, like a job crisis, an illness, or a breakup, disrupt sleep. Crucial are the perpetuating factors: behaviors and thoughts intended to help but worsen sleep in the long term, like staying in bed longer, daytime naps, or worrying about the next night.

This creates a vicious cycle: poor sleep generates worry, worry creates tension, and tension prevents sleep. Sleep research refers to this as hyperarousal, a state of heightened 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 about 2.6). More on this in our article Why poor sleep can make you depressed.

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 reacts with brief awakenings, often unnoticed. Typical signs are loud snoring, observed breathing pauses, morning headaches, and pronounced daytime sleepiness despite seemingly adequate sleep duration. The severity is determined by the apnea-hypopnea index (AHI): 5–15 events per hour are mild, 15–30 moderate, over 30 severe. Untreated, OSA is associated with hypertension, cardiovascular disease, and stroke; hundreds of millions worldwide are affected, many undiagnosed. Restless legs syndrome, rhythm disorders, pain, or medications can also cause sleep problems. With such indications, medical evaluation is needed before starting insomnia therapy.

What Helps with Insomnia? CBT-I as the First Choice 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 UK NHS, recommend cognitive behavioral therapy for insomnia (CBT-I) as the first choice 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 reconnects the bed with sleep: go to bed only when tired, get up if awake for long, set a fixed wake-up time. Sleep restriction temporarily reduces 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 don't change sustaining habits and thoughts.

The problem is implementation: only a fraction of people with insomnia ever receive CBT-I. Digital programs deliver the components in a structured way via an app and are now part of care: in Germany, digital health applications can be prescribed since 2020, and health insurers are including 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: based on CBT-I, CE-certified as a medical product in the EU, and studied in three University of Salzburg studies. 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 dropped 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 fell from 92 to 67%, and sleep diary showed sleep onset and nighttime wake time reduced by about a quarter each, while objective sensor data remained largely stable. Today, the program lasts eight weeks and is open for twelve weeks to realistically complete it in daily life.

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

The basis of any CBT-I is the sleep diary: bedtime, estimated sleep onset, wake phases, wake-up time, daytime condition. It captures 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 at night often perceive the night as significantly shorter than it was. This discrepancy is therapeutically valuable because it helps to check catastrophic thoughts against reality. Many consumer trackers underestimate short wake phases by more than 50% and often recognize sleep stages only near 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 total sleep time deviation of about 6 minutes (Topalidis et al., 2025, https://osf.io/preprints/psyarxiv/27wun_v1). More 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 problems falling or staying asleep 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 allow myself enough time and a suitable environment for sleep?
4. Do I feel impaired during the day because of it, such as being 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 issues, structured CBT-I is next. Medical evaluation 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 practitioner's office.

Frequently Asked Questions About Insomnia

What is Insomnia?

Insomnia is a sleep disorder where falling or staying asleep fails despite having enough opportunity, and the day suffers as a result. It is considered 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% occasionally have 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 choice therapy according to guidelines. In two randomized controlled trials of 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 dropped 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 techniques. Sleeping pills help only short-term, medically supervised, and usually not longer than four weeks according to guidelines.

What is the Difference Between Insomnia and Sleep Apnea?

In insomnia, the problem lies in falling or staying asleep with increased tension; breathing is unremarkable. In sleep apnea, breathing repeatedly stops during sleep. The 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 complaints, mood swings, or medications play a role, or if sleeping pills are regularly taken. The first point of contact is the general practitioner's office.

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