We present a new model of sleep regulation which integrates the two process model and the limit cycle reciprocal interaction model. In the two process model the interaction of a homeostatic process (S signal) and of a circadian process determines the timing of sleep and waking. In the limit cycle model, the NREM - REM sleep cycle is generated by the reciprocal interaction of two coupled cell population. The present model integrates the two considered models introducing the trigger REM - NREM generated by the REM-ON signal and activated when REM-ON overcomes the S signal.