Make sure your oxygen mask is fitted before helping others…
It’s the instruction given in aeroplanes in case of emergency, and used as a metaphor to encourage people to make sure they have what they need before assisting others.
The metaphor applies to viva prep too. You can’t help yourself if you’re not in a good place to begin with.
You need rest. You need space. You need time.
You need to be able to breathe.
Make sure you have your oxygen mask on before you help yourself get ready for the viva.