Sometimes there are days when you try to study and everything goes pretty well and you manage to prepare for all the exams and tests you are supposed to take the following days.
Sometimes there are days when you try your best but without result. Because the only thing you are sure about is the feel that your head seems to be going to explode in next several minutes and your brain is not willing to accept any other information.
Don’t worry. It can happen to everyone. Stop studying and take a break. If you can, take a nap or go to bed early if it is already evening and look at the notes once again later. The more you push on it and continue studying in that state of body and mind, the worse it will be for you because you cause harm to yourself and lose time. Personally, going to bed earlier and getting up earlier is one of the best things to do in that kind of situation. Tomorrow is another day.