Keep a tally of your viva prep. Every day you do something to help your preparations, big or small, make a mark. One mark per day, not one mark per task. Watch as the number of marks build over time.
If you’re pre-submission this could be a task as simple as downloading regulations or as big as finishing your thesis. After submission this could be marking when you write a few notes or have a mock viva.
Just one mark per day. Every time you add a mark you’re showing your commitment.
It’s a simple little message that you’re sending to someone: you, days or weeks from now on the morning of your viva.
Whatever else you feel, whatever else is happening, when you look at your tally you can see clearly that you’ve done the work.