Monophasic sleep schedules involve sleeping in one bout at night, while polyphasic sleep schedules consist of two or more bouts of sleep, either at night or during the day.

As we age, our sleep architecture changes, with infants experiencing highly polyphasic sleep, transitioning to biphasic and eventually monophasic sleep patterns in childhood.

The timing of sleep is critical; going to bed later can cut into deep sleep, which typically occurs in the first half of the night.

Polyphasic sleep, which involves multiple short sleep periods, has been shown to decrease overall sleep quality and can lead to impairments in cognition and mood.

Tracking sleep has revealed that many people underestimate how little sleep they actually get, often thinking they sleep more than they do.

Studies indicate that polyphasic sleep can significantly reduce REM sleep and overall sleep efficiency, making it an unwise choice for adults.

Co-sleeping has been a natural practice throughout human history, and dismissing it based on modern studies ignores the historical context of child-rearing. You have to be skeptical of scientific studies, as many are based on low-power research that gets over-applied beyond its context.

To support sleep and habit consolidation, maintain a dark and cool environment during phase three, and avoid eating too close to bedtime.

During the second phase of the day, 9 to 14 hours after waking, dopamine and norepinephrine levels decrease, while serotonin rises, leading to a more relaxed state that is beneficial for certain types of habit formation.