Hi Praveen Joshi,
Thanks for writing your query.
It seems that you are over exerting your body.
You should study but give breaks of about 15-20 minutes after every two hours of study.
You have not mentioned about your sleep pattern.
Best natural time for sleep is in the night.
At least 6-7 hours of sleep is sufficient to keep the body recharged for furthur work.
If possible take a nap of half to one hour in the afternoon. This will also help you in studies.
Also take care of your diet. Eat fresh fruits and vegetables to keep the body fit.
Drink atleast 8-10 glasses of water daily.
Avoid alcohol and cigarette.
Excessive tea or coffee to keep you awake is also harmful.
will also help in rejuvenating your body.
I hope this is helpful to you.