Awakening from different sleep stages, percentage of different stages of sleep subsumed within a sleep episode, and sleep episode length, have all been hypothesized to affect cognitive performance upon awakening. To further examine the contribution of these factors, 14 healthy participants slept for 3 h (0300-0600 hours) and 6 h (2400-0600 hours), with each sleep episode separated by 1 week. Electroencephalographic measures were taken throughout each sleep episode, and participants completed the Attentional Network Test, which measures alerting, orienting, and executive functioning (conflict) components of attention, upon awakening. Overall, mean reaction time (RT) was slower in the 3- and 6-h post-sleep conditions than in a baseline (pre-sleep) condition. Alerting, orienting, and conflict measures of attention did not significantly differ across the baseline and two post-sleep conditions. Awakening from REM sleep resulted in slower overall RT than awakening from lighter sleep (stages 1 and 2). In multiple regression analyses, overall RT was predicted by the duration of slow wave sleep (SWS), such that more time spent in SWS was associated with an overall slowing of RT. Conflict scores were predicted by the duration of REM; that is, more time spent in REM was associated with greater amounts of conflict (i.e., larger flanker effects). These data provide more information about the process of awakening and suggest that SWS and REM influence different aspects of attention upon awakening.