Modeling napping, post-lunch dip, and other variations in human sleep propensity.

HUMAN SLEEP PROPENSITY (SP) CAN BE DEFINED AS THE PROBABILITY TO FALL OR TO REMAIN ASLEEP AT A GIVEN POINT IN TIME. SP VARIES SYSTEMATICALLY within 24 hours with one major peak, which is normally associ-ated with a long and consolidated sleep phase, typically placed at nighttime and coinciding with low values of deep body tem-perature. In addition, SP shows a secondary, but minor increase half-way between 2 subsequent major sleep phases.