Delirium is usually more severe at night, so the patient will experience severe sleep disturbances. For example, insomnia, or in severe cases, complete sleeplessness or reversal of the sleep-wake cycle. Daytime sleepiness with increased nighttime symptoms and nightmares or dreaming, the content of which may persist as hallucinations until after awakening. Daytime wakefulness decreases and nighttime abnormalities increase, and the state vacillates between wakefulness-sleep, dreams and hallucinations. In mild cases, the patient may doze off during the day and have disrupted sleep at night; in severe cases, there is a serious disruption of sleep rhythm, which is also a common phenomenon in delirium patients and can be called “sunset phenomenon”, or “day-night reversal” as the common people can easily understand. In fact, besides sleep disturbance, delirium has many other manifestations. For example, “unconsciousness”, such as always ignoring the daytime, sleepy-eyed appearance; seeing or hearing some strange things and sounds; becoming unaware of family members, unaware of the time, unaware of where they are, etc.; unable to control speech and work; appearing mood changes and other phenomena different from usual. So, what are the possible causes of delirium? The cause of delirium is very simple to understand. It is an organic change in the body that affects the normal physiological function of the brain. In fact, delirium can be caused by any cause, such as the use of alcohol, drugs and certain medications, abnormal functions of major organs such as the heart, liver, lungs and kidneys, disorders of endocrine and nutritional metabolism, and disorders of water-electrolyte and acid-base balance. The elderly, in particular, are most likely to suffer from delirium due to all the above-mentioned reasons. In fact, delirium is very common in general hospitals, especially in intensive care wards, burn wards and geriatric wards. Of course, in addition to the organic factors mentioned above, psychological factors can sometimes cause delirium. The most classic example is the story of Fan Jin. Although the original text does not have all the evidence of whether Fan Jin was delirious at that time, “unconsciousness” in the original text should be considered as a disorder of consciousness, as well as “Well! Well! I was hit”, “out of the gate not much way, a kick in the pond, struggling to get up, his hair fell apart, both hands yellow mud, dripping all over the water. The crowd couldn’t pull him, patting and laughing, and kept walking to the set.” Obviously, the messy behavior and speech can be reflected. The author Wu Jingzi also mentioned in the article that “the crowd looked at the small eyes and said together: ‘So the new nobleman is crazy with joy.'” In fact, this can be interpreted as the diagnosis of “acute stress disorder” today. The connection between delirium and sleep. First of all, the sleep rhythm of delirium patients is usually disturbed, with shortened waking time during the day, sleepiness and drowsiness, and “awake” at night with agitation, so the normal sleep-wake cycle is disrupted or even reversed. At this time, it cannot be easily thought that it is just insomnia, or that it is because of the old dozing off during the day and cannot sleep at night. Secondly, the symptoms of delirium usually fluctuate lightly from day to night. However, we need to distinguish it from “sleep-wake rhythm disorder”, which is discussed in the relevant section of this book. Delirium is a more dangerous state, not only because of the behavioral and sleep problems it causes, but also because it indicates the severity of the underlying illness. The treatment of delirium is firstly the treatment of the underlying disease, secondly the symptomatic management of symptoms such as behavioral-emotional sleep, and finally the care of personal life. Therefore, when we find someone close to us in a similar situation, we should remember that we should go to the hospital promptly for consultation and treatment.