During which stage of sleep is an average adult most predominantly found in the first third of the night?

In the first third of the night, an average adult predominantly enters deep sleep, which is classified as N3 sleep. This stage, also known as slow-wave sleep, is characterized by high-amplitude Delta waves. It typically occurs shortly after falling asleep and is integral for physical restoration, memory consolidation, and overall health.

During N3, the body continues to progress toward deep sleep, which is essential for rejuvenation. In this stage, physiological activity slows down, and it's more challenging for a person to awaken, marking this phase's restorative properties.

While N2 and REM sleep certainly occur during the night, they do not dominate the early part as N3 does. N2 sleep is lighter and comprises shorter spindle bursts and K-complexes, while REM sleep, which is crucial for cognitive function and dreaming, generally occurs later in the sleep cycle, particularly in the latter half of the night. The "Awake" state is not classified as sleep and thus is not applicable to this question. Therefore, N3 is the stage of sleep where an adult spends the majority of time in the first third of the night.