People usually spend 1/3 of the day and night sleeping, i.e., they go to sleep at night and wake up during the day, forming a sleep-wake rhythm. Sleep-wake rhythm disorders are sleep disorders caused by a sleep-wake rhythm that is different from the usual one. The disorder is usually seen in adults, but is rarely seen in childhood or adolescence. Differential diagnosis of disorders of the sleep-wake schedule: allergic sleep: behavioral or physiological abnormalities during sleep. Primary insomnia: difficulty falling or staying asleep, or waking up feeling unresolved (feeling insufficiently rested even after normal sleep). Primary narcolepsy: Patients complain of excessive sleep, prolonged sleep or daytime sleep episodes. Episodic Sleep Disorder: Patients have uncontrollable sleep episodes with transient loss of muscle tone (sudden collapse). Note: Sudden collapse is the momentary entry into the REM sleep stage, and the symptom involves a REM disorder. Breathing-related sleep disorders: Excessive sleep or insomnia due to sleep-related breathing difficulties, including the following symptoms: Obstructive sleep apnea: The respiratory system is still active but airflow has stopped (snoring). Central sleep apnea: Short-term cessation of breathing, often associated with a central nervous system disorder. Mixed sleep apnea: A combination of obstructive sleep apnea and central sleep apnea. Symptoms similar to those of insomnia. Physiological rhythm disturbance sleep disorder: persistent or recurrent disturbances resulting in excessive sleep or insomnia, due to a mismatch between the patient’s 24-hour sleep-wake rhythm pattern and the rhythm required by his/her environment. Night terrors: Most often occur in children and are not a health risk. Typically, night terrors occur during the child’s fourth sleep stage, when the child has difficulty waking up, but will scream in response to the shock. When the child eventually wakes up, he or she may still feel fearful, but cannot remember exactly what sleep psychological activity occurred that caused the night terrors.