I've run across a couple of books indicating that 'bimodal' (two periods of sleep) is normal. Through the Middle Ages, people would go to sleep at sundown, wake up after a few hours, be awake for a bit (the Church had recommended prayers for the time between 'First Sleep' and 'Second Sleep').

I'd thought that maybe that was the way we were all supposed to sleep - but I've seen no evidence of this sleep pattern through the rest of history (Herodotus on forward).

However, if you look at how people in primitive, essentially pre-contact' tribes sleep, it's bimodal - not the Medieval two sleeps pattern but a sleep period at night, starting after darkness as temperatures start to fall, then another sleep in the heat of the afternoon.

So... if anyone questions your napping, tell them it's 'Paleo'. :-)