Our bodies are programmed to know when it’s time to sleep and when it’s time to be awake. This internal “clock” is what is referred to as circadian rhythm. Our circadian rhythm signals changes in our bodies that make us realize when it is time for bed, as well as when it’s time to be awake and productive. Granted, it’s more complex than that, but the general idea is that our bodies are designed to perform certain functions at a given time.Get more information here. http://www.psychologytoday.com/blog/day-in-day-out/201211/why-do-we-sleep-when-we-do
Looking back throughout human history, it’s fairly easy to see why people adapted to sleeping at night and working during the day. However, unlike our ancestors, the modern world doesn’t stop when the sun goes down. Many of us are on the job in the wee hours of the night.
Although our society has evolved to 24/7 activity, our bodies have not been quite so willing to follow suit. For the person who works the graveyard shift or alternates between day and night shifts, the effects of a work schedule being out of sync with one’s body signals is often readily apparent.
Changes in our normal wake/sleep cycles can disrupt circadian rhythms. As a result, shift workers may experience one or more of the following symptoms: daytime sleepiness, headaches, fatigue, and a feeling of tiredness even after getting adequate sleep.
While there are steps that can be undertaken that will alleviate some of the symptoms, it may be difficult to win the battle against your natural instincts when it comes to the sleep/wake cycle.