there is interesting historical research, which pops up from time to time, showing that people in many cultures before the advent of electric lighting commonly slept in two phases -- about 4 hours, a couple hours awake, and about 4 hours.

i think it gets too strong when people claim that this is "natural" or "better" or something. but the historical evidence suggests it's at least "okay", and if you sometimes wake up at 3am maybe just embrace this, get up, do something tedious, and go back to bed.