Sleeping at night vs sleeping at day

Sleeping at night is generally better aligned with the body’s circadian rhythm: humans are biologically oriented toward daytime wakefulness and nighttime sleep, and shifting to a nocturnal schedule can carry mental and physical health costs. 1

• Daytime sleep and body-clock disruption: Sleeping during the day can be difficult when it conflicts with your internal timing and the natural light-dark cycle. Shift workers are advised to keep their schedule consistent where possible; rotating shifts can disrupt health-related rhythms and well-being. 2
• Health and light-dark timing: Deviating substantially from a daytime-awake, nighttime-asleep schedule has been associated with serious mental and physical health effects. Daylight exposure and darkness at night are each linked with better mental-health outcomes; nighttime darkness also supports regular sleep timing. 3 4
• Deep and REM sleep; naps: Sleep timing affects how much slow-wave and REM sleep occurs across the night, and losing sleep can affect emotional regulation. Short naps can help, but they are not presented as a replacement for a well-timed night’s sleep. 5 6
• Daylight, darkness, and emotional regulation: More daylight exposure—especially in the morning and during the day—was associated with fewer mental-health challenges, while dim or dark conditions at night were also associated with reductions in symptoms. Darkness helps signal sleep onset; the benefit described is darkness while asleep, not staying awake in the dark. 7