Hello, I Am 25 Yr Old Studying For Various Govt.

Hello, I am 25 yr old studying for various govt. exams and I need to concentrte for long period in a daytime. But from last few days I am suffering from dizziness, light headedness & sleepiness in a day time. A day before I feel so I strted to eat more than my previous diet. I took some non vegeterian stuff too and also due prolonged night study I couldent complet my sleep as well. So I want to know the reson behind my ailment & how should I overcome from it. Also suggest any diet pattern (and medication if needed...) to avoid such obstacles.
Than You.