Insomnia can be broadly divided into two categories according to the duration of the disease, namely transient insomnia (1 month). In general, insomnia that lasts for more than 1 week in a row has a tendency to be chronic. For transient insomnia, if it is not caused by jet lag or shift work, it is regulated insomnia. This type of insomnia has a clear trigger, which is a sudden increase in arousal state induced by acute stressors. Common stressors include stressful life events such as loss of a loved one, divorce, unemployment, hospitalization, and changes in sleep environment such as sleeping in unfamiliar surroundings. Approximately 10% of the population suffers from chronic insomnia. The typical person with chronic insomnia has episodic insomnia in the early stages, which later becomes frequent and finally evolves into daily insomnia. The duration of sleep on the day of insomnia is also gradually reduced. Some patients with chronic insomnia also have a cyclical nature to their symptoms. Although these patients may have primary insomnia, most of them have insomnia secondary to or associated with other causes. Primary insomnia accounts for about 1/4 of all patients with chronic insomnia, with acute or insidious onset and more women than men. It can be further divided into idiopathic insomnia, paradoxical insomnia and psychophysiological insomnia. Idiopathic insomnia This type of insomnia usually begins in infancy or in younger children. The patient has a chronic sleep disorder, but no clear cause can be identified. It accounts for less than 10% of all insomnia visits to sleep clinics. Patients complain of difficulty with sleep onset or sleep maintenance; or report inadequate sleep duration. Impaired daytime function is consistent with the degree of sleep loss. This type of insomnia may be related to an intrinsic defect in the structures responsible for the sleep-wake cycle within the central nervous system. The onset is insidious, chronic in course, and lasts for life without periods of remission. Treatment is difficult, and patients may rely on sedatives or alcohol to aid sleep. Patients may complain of daytime fatigue, difficulty with attention and concentration, and an increased risk of depression. The diagnosis relies on ruling out other causes of insomnia. Paradoxical insomnia This type of insomnia is also known as poor sleep state perception or subjective insomnia. It accounts for less than 5% of people with chronic insomnia. It usually occurs in young and middle-aged people and is more common in women. The clinical course tends to be chronic, often complaining of insomnia for several years. Patients do not have impaired daytime function consistent with complaints of severe insomnia, although they complain of chronic severe insomnia, and if polysomnography is available, no significant sleep disturbance can be identified. Patients are unable to identify total sleep duration with certainty and often overestimate sleep latency and underestimate sleep duration. Patients may report little sleep or almost no sleep overnight, but are energetic during the day and do not nod off. Patients “perceive” their environment or have a continuous thought process for most of the night. Chronic sleep disorders lead to mood disorders such as depression or anxiety. Patients often use excessive sedation. Psychophysiological insomnia Patients have inappropriate sleep-preventive behaviors that occur and eventually progress to become a major factor in sensory sleep disorders. Although the onset of insomnia is associated with a particular stressor, the sleep disturbance persists long after the stressor has been eliminated. Before going to sleep, the patient is irritable, hypertonic, and mentally awake with persistent intrusive thoughts. He/she is neither able to relax nor to stop thinking about it, and is overly concerned about falling asleep. A vicious circle is created in which the patient tries very hard to sleep → tension → more arousal, anxiety → further reduction of sleep tendency. Sleep comes easily when the patient is distracted or does not make a conscious effort to sleep. Interestingly, patients often report sleeping better in any other place than in their own sleeping place. Many patients have a lifelong history of intermittent light or poor sleep. It is usually chronic and can worsen progressively if left untreated. Patients have increased daytime sleepiness and heavy fatigue. There is a greater risk of depression. Patients have a tendency to overuse sedatives.