(They need to have a 'Newborn' topic on this site. I feel bad whenever I post questions of this nature in 'Pregnancy')
Is it common for newborns to fall asleep very suddenly?
My 6-week-old has been doing this since a few days of life, I think. One minute he's awake and alert, the next minute (almost as if someone snapped their finger and made it happen) he's asleep. It'll often happen when he's halfway through doing something, such as grunting/straining during a bowel movement. He's even been known to fall asleep in upright positions, such as when I'm burping him. Once he's asleep his face will become very animated - smiling, movement of the lips/mouth, eyelids opening and closing (which is often the case when he's asleep). The sleep seems to be very light, though, because he wakes again at the slightest jerk or if something startles him such as a loud noise.
Starting to worry about narcolepsy now... Kind of hoping this is just one of those weird, random newborn things...