Stardate 2262.816

The transfer has been completed. Bones and the androids agree that the process went as well as could be expected, but it could be hours or days before we know how successful it was. Bones explained that, even though Chekov's physical problems are no longer an issue, his brain needs time to catch up to the fact that he's no longer dying.

I suppose that makes sense since there was no way to explain what was about to happen to him. Waking up inside a new body would be disorienting to say the very least.