I haven’t met many PhD graduates or future viva candidates who weren’t at least a little nervous. Nervous is very common; if you feel it before your viva then you’re in a pretty normal state.
But feeling nervous isn’t usually comfortable.
We can distinguish between good nerves and bad nerves, the former before a happy event, the latter before something unwanted. In both cases there’s probably a degree of importance with the event. Nervousness and importance are correlated, two factors braided together in life’s tapestry. What if… something unexpected happens? Or what will happen? What if something goes wrong?
So nervous is normal for the viva. Nervous is sort-of expected given the nature of the viva.
Nervous doesn’t have to be all you feel though. You can feel excited: the viva is one of the last big things to do before the end of your PhD. You can feel knowledgeable: you know your work and your thesis. You can feel talented: you must be capable to get this far.
You can feel confident you are in the right place, ready to act.
Nervous is normal for the viva. Many, many more emotions could be normal too.