The circadian rhythm is more commonly known as the body clock. This internal rhythm of the body is normally 24 hours but gets adjusted by external factors such as sunlight or bright lights. For people who have a normal circadian rhythm they can fall asleep after it gets dark outside and wake up 7 or 8 hours later without any problems.
 

Most people can adjust their sleeping schedule without experiencing any negative consequences and some actually prefer to either stay up late or get up early. But for those who sleep at the wrong time and get sick, they most likely have a circadian sleep disorder. This inflexibility makes it hard to make up for lost sleep during the day when they might have lost sleep at night. There are six types of circadian rhythm sleep disorders including:
 

• Delayed sleep phase

• Free-running

• Advanced sleep phase

• Irregular sleep-wake

• Shift work

• Jet lag
   

  Some common symptoms associated with these types of sleep disorders include difficulty initiating sleep, sleepiness during the day, not feeling rested after getting sleep, and a decrease in cognitive skills. Some recommendations for managing circadian rhythm sleep disorders include proper sleep hygiene including having a dark, quiet, and comfortable bedroom, using background noise when sleeping, light therapy and taking melatonin.