Qn. "Is there a link between body clock and one’s moods? I am told if these two issues are not monitored they may result into mental disorder".
The simple answer to your question is yes. That said, you need to understand the circadian rhythm (or the body clock) and how it functions in the average person.
To put it another way, it is important to appreciate why and how the body functions in different ways across the 24 hour day cycle. The body is regulated such that at different times of the day, it is optimally ready to perform the tasks put before it at the relevant time.
At midnight for example, most (not all) people are asleep. In this arrangement (as is well known by house burglars), by 2am, the individual is in their deepest sleep. During this stage of deep sleep, the body lowers the temperature, blood pressure and pulse because there is no need to fight or flee. The body is in the resting stage and it is saving its energy reserves for later in the day. It is most difficult to wake the sleeping person at this time (2-4am).
At daybreak, the body releases massive amounts of "wake up hormones" (cortisol) and shuts off sleeping hormones (melatonin). This is the time for most rapid rise in physiological parameters, namely blood pressure, pulse rate and breathing rate. As the body prepares for the alertness required for the daytime activities, there is often a queue to the toilet as many people need to open their bowels at this time! The whole body including the digestive system wakes up.
In the course of the day, and with blood pressure, pulse and other parameters in full operative mode, the hunter is ready to go out either to bring down a gazelle for lunch, or strike a deal with a business partner at the bank.. From about 10 am to early afternoon, the body and mind reach peak performance. As the day progresses further changes take place and the highest blood pressure readings and temperature occur towards the end of the day.
As one goes to watch the 9 pm news, many people emit a yawn, and declare that they have had a long day and will watch the news and go off to bed, read a little and then sleep. During news, at 9 pm, the release of melatonin starts and the body begins to wind down. Even bowel movements go to sleep ready to crowd the toilet in the morning.
This rather lengthy lesson in physiology is intended to demonstrate what happens in the bodies of the majority of healthy people.
There are however millions of healthy people who do not follow this pattern. Some describe themselves as early morning people who function best from 3-4 am, and are out of action by 7 pm.
Similarly, there are people for whom 9 am is an early time to wake up and they have to remain awake (sometimes at work) until 11 pm. Both groups are normal, but not in the majority. Poor physical and mental health can cause changes in the system.
In view of the fact that most people who commit suicide do so in the context of a depressive illness, Psychiatrists have over the years taken a great deal of interest in the time of day that suicides occur. One long term study in the USA showed that suicide rates were at their lowest between 4 am and 8 am.
Looking at the circadian rhythm as described above, this is the time of the release of "wake up hormones". In another study from Italy, the worst time for suicide was on Mondays between 8 am and 11 am! This is the time to get up and hunt.
It must be clear from these and other studies that there is a link between the biological clock and mood.
Your second concern is less certain. There is no evidence that not monitoring the body clock leads to any form of mental illness.
What is clear is that awareness of mental health issues in general leads to early diagnosis and treatment of mental illness which leads to better outcomes.
Simply put, awareness of what mental disorders look like can get you treated early with better chances of getting better!