Watching Out
You can’t eliminate every potential stressor or difficult question ahead of your viva but through preparation you can be aware of them.
Read your thesis and reflect on your research. What was stressful? What was difficult in a negative way? Was there anything over the course of those years that made doing the work difficult?
Ahead of your viva you can prepare for engaging with those topics if they come up at the viva. You don’t have to say everything but you might have to say something that you’re uncomfortable talking about.
Writing some notes beforehand, talking with your supervisor or a trusted friend or even using the mock viva as a way to prepare can all be useful steps to getting ready if there’s a sensitive topic.
You can’t remove difficult topics from the viva conversation. You can be aware, you can watch out and prepare to engage well.