Have you noticed one thing in your life?
When you are about to complete your lessons, you say that you are getting a sound sleep. You also start saying that your mind is full of thoughts on various games, the activities relating to your friends, the cinema you had seen yesterday etc. etc.
You could have noticed this also in your life ?
When you are at a cinema hall or when you are actively engaged in any sports activities or when you are with your friends, you are not getting any thoughts relating to your lessons or studies ?
It is the natural tendancy of the mind - to keep away from a work which seems to be very difficult for it.
However you can control your mind. Just like a sports activity, or viewing a cinema, you can also engage in your studies without any disturbance from any thoughts.
It is by sheer practice. Learn to control yourself. Once you had determined that you had to complete any work within a stipulated time, concentrate your energies and put your heart and soul into the work you are engaged in. Nothing is difficult. This you can practise within a week or ten days. Once you had mastered to control your mind, you can master any amount of your activities.
Success lies mostly in controlling our mind and our thoughts.