I think its worth to note that the further the Doctor regenerated, the more trouble he had to cope with that, when outside the TARDIS. In his fifth and eighth bodies, he suffered greatly, and even the sixth, seventh and tenth bodies he struggled greatly. So that Rassilon or something else had something to do with that process is not exactly out of the question.
"Spock...?" Kirk said, whispering.
"I am... most pleased to see again, Captain" Spock formally replied.
McCoy shook his head in disgust. "Oh, for crying out loud, Spock. Its been eighty years!"
"Seventy eight point four years, Doctor."
The Holy Three meet again, in The Return