Unirytmi

Unirytmi (sleep-wake rhythm) is the recurring pattern of sleep and wakefulness in humans, largely determined by the circadian clock and the homeostatic drive for sleep. It sets the timing, duration, and architecture of sleep over roughly 24 hours. The central pacemaker is the suprachiasmatic nucleus in the hypothalamus, which coordinates peripheral clocks in tissues. Light exposure, especially morning light, synchronizes the clock via retinal pathways containing melanopsin; melatonin secretion by the pineal gland signals readiness for sleep in dark periods. Process S describes the accumulating sleep pressure when awake and its dissipation during sleep.

Individuals show variation in unirytmi, with chronotypes ranging from morning-type to evening-type, and this can shift with age, environment, and health. The typical adult sleep window spans 7–9 hours, but individual needs and timing vary. Disruptions to unirytmi occur when there is chronic misalignment between internal timing and external demands, or when the clock fails to respond to cues. Circadian rhythm sleep disorders include delayed sleep-wake phase disorder, advanced sleep-wake phase disorder, irregular sleep-wake rhythm disorder, non-24-hour sleep-wake disorder (mainly in blind individuals), and shift work sleep disorder, as well as jet lag after rapid time-zone changes.

Assessment commonly uses sleep diaries, actigraphy, and, if indicated, polysomnography. Management emphasizes regularity and synchronization with the environment: timed light exposure and darkness, sleep scheduling, sleep hygiene, meal and exercise timing, and, in some cases, pharmacological aids such as melatonin or chronotherapy. Understanding unirytmi supports considerations of performance, mood, metabolic regulation, and overall health, given that repeated circadian disruption is linked to adverse outcomes.