You were asking for historical backing. Sleep is definitely abundantly mentioned in historical writing, while segmented sleep is not. I take the absence of the latter as historical backing.
This is tantamount to saying that the Egyptians from the 18th Dynasty onwards did have horses but no black or white ones because while the historical records concerning warfare did mention horses a lot, nowhere is there a mention of black or white horses. I conclude the ancient Egyptians only had brown horses q.e.d.
