Just some random thoughts about biphasic sleeping:
My tiredness level throughout the day seems to be the opposite of what it was when I was going monophasic (1 sleep period per day). While before, I would get more tired as the day went along, I now am very tired after waking up (some days it is really quite hard to wake up), but as the day goes along, I feel better and better (although I am still generally always tired throughout the day). Most days, it takes a little bit of effort for me to go to bed, since I am generally working well on a project, or just enjoying a nice evening.