It’s always worth saying: yes, you can have a break in your viva.
A bathroom break.
A medically necessary break.
A break to breathe and relax or compose yourself.
An hour in, two hours in, three hours in, it doesn’t matter when.
Your examiners might offer, but you can always ask.
Then at the end of your viva, most likely, one more short break while your examiners discuss the outcome. They exchange notes and reach their final consensus.
For that final break decide in advance what you might do, so that you aren’t sitting and wondering about what just happened and what is about to happen.
And hopefully when your viva is finished you can take a longer break that is solely about relaxing and resting.
