You don’t need to recall all the details of every day of your PhD to pass your viva. You don’t need to have memorised every page of every paper you have read when you talk to your examiners – or remember every page that you have written for that matter.
Of course, you need to read your thesis to prepare for your viva. It help to review what you’ve done and consider likely areas you’ll discuss. It helps to have a way to remember what’s really important.
But, more importantly, you need to remember that you did the work.
You need to remember what the viva is really for.
You need to remember what your viva and what success means to you.
And you need to remember that there are lots of things you could do to help you remember the things that matter the most.