Chris Chibnall has shared a short story on the Doctor Who site that reveals the specifics of the Doctor’s post-regeneration survival. The story “Things She Thought While Falling” reads like a flavor document meant to help Whittaker internalize the then-new Doctor’s voice:
That’s interesting, she thought. I seem to be an optimist. With a hint of enthusiasm. And what’s that warm feeling in my stomach? Ah, I’m kind! Brilliant.