How does homeostatic sleep pressure build during a day of wakefulness?

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Homeostatic sleep pressure is a fundamental driver of the sleep-wake cycle that increases progressively as the duration of wakefulness extends throughout the day. This accumulation of pressure typically results in a person feeling increasingly sleepy as the day progresses.1

For a typical adult, this homeostatic process is balanced by the circadian rhythm, which provides support for wakefulness during the early evening hours. As this circadian support subsides later in the evening, the homeostatic sleep pressure is left unbridled, which leads to the onset of sleep.1