It might take a lot of re-reading to remember something that you need to know. On the morning of my viva I knocked on my supervisor’s door to check the definition of something I had been using in my work for over two years. I tried and tried but it just wouldn’t stick.
It’s not trivial to build up a mental model of the knowledge you need for your research. What’s harder is building up the certainty and confidence that you are good enough, that you’ve done enough. You might need to repeat that over and over to yourself. You might have to reflect and review and consider many times to see that you’ve done enough.
Survive means manage to keep going in difficult circumstances. If you get to submission, if you’ve got this far, then you’ve got through enough to show you can succeed in the viva.
For the hundredth time: if you’ve got this far then keep going.