Im Studying For My Boards, Which Requiere Many Hours A

im studying for my boards, which requiere many hours a day... after a few hours.. i feel dazed and i cant focus...I physically dont feel tired but its like what i read isnt sticking. people say rest, yet I slept 8 hours and still next day I start to forget where I pump my gas.where i placed my keys ...etc.
I rest 3 days full with no studying I feel refreshed but its like starting over.
what can help me with controling not get into daze while still being productive towards studying for boards. and when i feel like that should i sleep rest.. and if next day i feel dazed how youd recommend doing instead of taking 3 days off . thanks