A person who normally sleeps eight hours a night sleeps less than five hours for two consecutive nights. On the next night, the person sleeps about nine hours. What is most likely to occur in that nine-hour night?

While NREM sleep is essential and may increase due to the body's need for restorative sleep, the focus after sleep deprivation specifically shifts towards REM sleep. Therefore, a higher percentage of NREM sleep is less likely compared to an increase in REM sleep following recovery sleep.

Slow-wave sleep, a stage of NREM sleep, is important for physical restoration and is likely to occur during recovery. However, the unique response to sleep deprivation emphasizes the rebound effect on REM sleep, making it less probable for SWS to dominate the recovery period.

In recovery sleep, individuals typically experience fewer awakenings as their body seeks to consolidate sleep and restore lost stages. An increase in awakenings would contradict the body's need for restorative sleep after deprivation.

The typical sleep cycle duration is generally stable at around 90 minutes. While the distribution of sleep stages may change, the cycle length itself does not significantly alter in response to sleep deprivation or recovery sleep.