You have time to press pause before you prep. You can put your completed thesis to one side and come back to it when you have had time to restore yourself. You can’t help yourself get ready for the viva if you don’t help yourself into a good condition more generally.
It’s general viva prep advice to pause and rest at submission, but essential if you reach submission and are tired by all you’ve had to do. If you feel worn down then a single day off is not going to help you get in the right frame of mind to read your thesis or prepare for a mock viva. Rest and take the time you need to get ready to prepare.