i went through the same phase once, reading things again and again over and over and yet brain registers nothing. well it's a phase first of, so relax it will pass. i would suggest, first make sure you are having plenty of rest. second, lit a pleasant scented candle, clean up your table, make an easy to do list for yourself. calm yourself and then sit to study, with a pen and markers. make notes parallely and make them colorful. do the diagrams. do not panic. relax and try to enjoy things you are doing. also have apple or green tea alongside or you can enjoy any other beverage that lifts your mood. i suggested then bcz they are healthy for brain and refreshing. all the best💕