Don't psych yourself out. Its all repetitive. There's only so much you can know about the CIA triad, OSI model, etc. I would say to just focus on your weak areas. For the CISSP mine was the SDLC, so I didn't focus too much on the other domains.
Keep on pushing, it doesn't have to be a sprint to get the cert, can be a marathon if that makes you feel better about grasping the information.