If it helps you to think of the viva as a one-shot, once-in-a-lifetime super-mega-event then keep going.
If that motivates you then stay motivated and do what you can to get ready and be present with your examiners.
But if thinking that way leaves you stressed out, then figure out a new story to tell about your viva. You don’t have to downplay the importance, but you can remind yourself you got this far by working hard and being good at what you do (there’s no other explanation).
The viva is a big day, maybe a challenging day, but it’s just one day. It comes after many other challenging days of your PhD.