Waking up with a jerk

Hey, Matt:

Why is it that when I'm just beginning to drift off at night and fall asleep, suddenly, BOOM, in my dream I trip or fall or get hit by a bus, causing my body to respond by jerking spastically, which wakes me up?

-- Dreamer, Encinitas

Veeeery interesting. Come into the Alice Institute for Dream Analysis and Advanced Spackle Research and curl up on the couch while we poke through your psyche. That just-falling-asleep, surfing-the-alpha-waves time is an odd blend of sleep and waking. Dream content and bodily sensations still interact to some extent. This is unlike dreams experienced in deep sleep, when motor neurons fire but are normally blocked from activating our muscles (so we won't dream about driving to Cleveland, and then actually get out of bed and do it). Speculation is that either an external stimulus or intense dream image can wake us more easily in the first stages of sleep, and in response we suddenly reestablish full brain-body connection with that characteristic jerk.