[Bluh explaining time travel.]

One of the things...we thought we could fix, that would make things better...Goku died not long after he came back to Earth, of a heart virus. Sudden onset, no cure--not at the time, anyway.

I came to warn everyone, but I also came to bring back medicine to save him.

[...and if you knew anything of time travel theory and the whole 'eliminating a timeline via paradox' thing, that might be particularly disturbing.]