Don’t keep your viva worry bottled up in your brain where you can merely be anxious about it.
Write it down. Tell a friend. Talk to your supervisor.
Your worry could be unfounded. Talking to someone who has had their viva or knows about the process could put your concerns in perspective. They could help you see what you can do to help yourself.
Your worry could be easily resolved. Being clear with yourself and knowing what’s wrong and could allow you to move forwards.
Your worry could be a tough situation – in which case exploring what you could do and what you will do, possibly with support from others, will allow you to work past that worry.
It’s natural, given the importance of your viva, that you might have worries. If you do then you can also do something about them.