Nick Ryder wrote:
True - he liked how he was as Tennant but why would he say 'I don't want to go' he could have just glowed out and disappeared like the rest of the timelords too. While yes I think he didn't want to lose his old self - when he's the last of his kind, who knows if his next regeneration is going to be his last or if that radiation he took in was going to regenerate him properly. He staved off a regen when he still had that hand in a jar - that was something no other Doctor did prior.
Jon Pertwee's Doctor got a massive radiation dose and he needed another Timelord's help to regenerate into Tom Baker's 4th Doctor so that could have Tennant's Doctor's concern.
Same as Peter Davidson's Doctor, he wasn't sure if he was going to regenerate.
On a side note it was a little crazy for Davidson's Doctor to set the TARDIS in motion when he was concerned that he might not regenerate. Peri would have been trapped in the TARDIS with a dead Timelord.