Human sleep cycles were once thought to be under the exclusive control of Circadian Rhythms. These cyclic patterns are the result of changing melatonin levels in the bloodstream, controlled by the Suprachiasmatic Nucleus (SCN) which is part of the hypothalamus. Much like the Pineal Gland, the SCN reacts to changes in light levels, which synchronize the Circadian Rhythms, and thus human sleep, with the local environment.

Circadian Rhythms are driven more than just a reaction to light, research shows there is an actual biologic counting process. Twenty-six years after their discovery in fruit flies, the first clock regulating proteins were discovered in mammals in 1997. A series of these proteins create a primitive counter whose period is set and reset by the body's reaction to light stimuli and physical activity. While this process was accepted as how the rhythms function, it still does not explain how they trigger a wake-up alarm.

Researchers in Germany's University of Lubeck have recently discovered another biological process that serves as the alarm for the 'body clock.' Test subjects anticipating a scheduled wake-up experienced an increase of adrenocorticotropin hormones one hour prior to rising. Patients that were not scheduled to arise experienced no such hormone boost. Normally, this hormone is secreted to stimulate the adrenal cortex when the body is under stress. In the case of awaking from sleep, the adrenaline boost rouses the brain back to consciousness and subsequently energizes the body.