Technically, with the amount of debunking that your brain does during REM Sleep, the human brain is usually more active during REM Sleep, whether that be at Day or at Night. <br /><br /> Generally though, individuals tend to sleep at night due to the circadian rhythm that most all humans follow. Technically, with the amount of debunking that your brain does during REM Sleep, the human brain is usually more active during REM Sleep, whether that be at Day or at Night. Generally though, individuals tend to sleep at night due to the circadian rhythm that most all humans follow.