Why do we fall asleep when studying?

First semester is coming to an end and all are getting ready for the end semester exams. So I thought of something which will be useful for most of us.. Now all are studying and one of the most common problems we have is falling asleep while studying. Actually why do we fall asleep when we study? Sometime we wait in bed for hours till we fall asleep but when going to study, we fall asleep within minutes. So why is this happening? Here is the answer..
It is because of a function in our brain. I will try not to make this a biology lesson, so in brief this is what happens inside our brain. Our brain needs lot of ATP to function. (For now, think it's something like a currency of energy and it is what keeps brain awake and the body functioning). So when brain using ATP it converts into ADP. So when we start using ATP rapidly (for an example studying) more and more ATP converts to ADP. This ADP can't keep pace with the energy demand so the brain functioning becomes dull. So it will be difficult to stay awake and study. This is why we fall asleep. And while we are sleeping ADP converts into ATP again and that's the reason behind feeling good after a sleep. And this cycle continues. If you have gone through how to study articles on net, this is the reason they always tell you to take 10 minutes breaks per like 20 minutes. It's an interesting fact ha?

I'm sure most of you are like this now :)

In my next few posts I'll try to give some knowledge about getting ready to end sem exams properly and how to score more. Some will be from my own experiences and others are what I have read. So stay tuned..!!