And this is probably no accident, for we are daytime creatures, biologically and psychologically geared for daylight activity. Body temperature is lowest at about 5 a.m., and melatonin, which makes us feel sleepy, begins to increase after 10 o'clock at night. Scientists at Cornell University recently reported that they were able to reset a person's biological clock by shining a bright light on the back of the knees, suggesting a more complex physiological basis for circadian rhythms than had previously been supposed. As production and other economic activity expanded into darkness, our biological clocks underwent stress. Many people do not function well at night.
Some report having a hard time eating, others can never adjust to sleeping during the day.
I was tired all the time. I became obsessed with sleep. The impact goes beyond unpleasantness or inconvenience. Some managers report increased illness, especially more colds and flu in the winter. And a wealth of studies shows that both accident and productivity rates worsen at night and that night jobs impose added health risks.