Listening to the audiobook for Chariots of the Gods (1968) the last few days and its genuinely pretty good: . MUCH more researched and logical than the Ancient Aliens tv show.
The author mentioned why did Egyptians think they needed to be mummified to be resurrected? And it got me thinking.
I'm agnostic when it comes to ancient astronauts.
However, let's say ancient astronauts ARE real. The problem with freezing a body to revive it later is that the water crystalizes when it freezes and causes major damage. If someone was doing long-term hibernation (to travel light years, possibly), it would make sense for them to dehydrate the human body, then rehydrate it before waking or resurrecting them from hypersleep.
Perhaps the ancient egyptians saw this happening with the ancient astronauts and tried to mimic it by mummification.