You’re so close at submission. It may not feel it, but the vast, vast majority of the work you need for your doctorate is done. Months upon months of hard work and you’re almost there…
…but you’re not yet. Yet. You will be soon.
Rest, ready yourself, read your thesis, rehearse for the viva, do whatever you need to so you feel good for this big, important day. You’re almost there, and it won’t take much to get there, or take much while you’re there.
Your viva isn’t the most important thing that you’ll ever do. Your viva isn’t the peak of your PhD.