If it’s hard to get started on viva prep or you’re putting it off then perhaps you need to make a plan – not to procrastinate but to give yourself some structure.
If you get distracted then maybe you need to put distracting things out of your reach.
Perhaps set a time to do some viva prep and set a time afterwards to do something that feels fun or like a reward.
And if the work feels like too much for right now then maybe you need to rest before you get ready for your viva.
Actually: remember that rest is part of what you need to get ready for your viva.