Circadian rhythms affect body temperature, hunger and alertness as well as sleep timing.

The longer version

Body temperature follows a daily curve, peaking in the late afternoon and dipping before dawn; hunger hormones, digestive activity and reaction speed all ride similar waves. Hormone release, blood pressure and immune activity follow their own daily patterns as well. Sleep timing is only one output of a system that schedules the whole body.

Because each function has its own preferred phase, alertness and temperature can drift apart during night shifts or long travel, which is why mental performance sometimes feels out of step with the clock on the wall. Records of workplace accidents and of athletic performance both show time-of-day effects consistent with these internal schedules. Plants and insects show comparable daily programs.

Where this entry sits

This collection gathers curious details about sleeping and dreaming, from nightly brain stages and body clocks to naps, yawns and unusual animal habits. It also covers how bedtime customs have changed across centuries, without offering any advice. The full list sits on the Sleep and Dreams page, where every entry is listed in order.