[weilawei]

Your comment about taking a quick nap is really insightful. I have a little experience with this. From my parents, I acquired the habit of taking small naps. Riding as passenger in a car puts me instantly to sleep (luckily, the same does not apply to driving). I also do this as a general thing--my sleep is more polyphasic and irregular than most people I know. I may be awake at virtually any point in the 24-hour cycle, but not necessarily at the same points each day. Overall, I find that I get about the same amount of sleep, but the odd hours allow me more concentration on work.