Originally Posted by Mark.:
“What people are missing is that The Doctor thought he was going to die completely.
It wasn't until he encountered Ood Sigma after speaking to Rose he realised he was about to regenerate (the line about the song ending, but the story going on).”
He seems to have thought prior to the episode that the prophecy could mean permanent death. Might even have thought it when entering the box (though I'd expect he'd realise it's something his body can cope with through regeneration- it's not as powerful as absorbing the energy from the heart of the Tardis like last time).
But as soon as the cuts on his face healed, standing outside the box, he knew it was a regeneration. He even said 'it's started'.
Originally Posted by Captain Stable:
“To be fair to the script writers, they did add that scene where he discussed the fact that regenerating does feel like dying - and even Classic Who treats it like this - Pertwee hates Troughton (the comment in Five Doctors "Oh no, not him again." as well as their first meeting in Three Doctors).
But I agree with Shineyteapot that the whole rant was wrong.
Did 5 know he was going to Regenerate?
Did 9 know? After all, he did say "I absorbed all the energy of the Time Vortex. And no one is meant to do that"”
Thankyou Captain Stable
To answer your questions- 5 wasn't sure, he said it felt different. He didn't know if he was going to regenerate or die.
9 knew he would regenerate as soon as he'd kissed Rose- he told Rose it was a way of cheating death, and that he would change. Whether he knew beforehand I couldn't say- and I don't get the impression he even thought about it- he was only concerned with saving her.