The Ancient Egyptians slept on pillows made of stone. Could it be possible to ever sleep on a stone pillow for one full night and wake up completely rested?

This is simple enough to try yourself..

If that's the only pillow you - or anyone you know - has known your entire life, then of course you'll get a good rest on it.

I suspect that if you gave one of those ancient Egyptians a feather pillow to sleep on, they'd toss it out after just a few minutes.

Back when I was a young man, I was stationed in Japan. Many/most Japanese slept on wooden pillows. These were not just lumps of wood, but were carefully crafted, shaped and finished wooden pillows. Now, I wish I had brought one home---what a conversation piece.

In the Army spent weeks in the field sleeping on the ground. We would come back to a comfortable barracks and most of us would sleep on the floor---the beds were to comfortable.

Sounds like you just answered your own question buddy.

I've slept on the ground using a 'steel pot' helmet and kevlar helmet for a pillow and slept very well.

I still sleep better on the ground or floor than I do in a bed, but my wife still wants me to sleep with her and she won't sleep on the floor, so I sleep in a bed.