Eleven young adults had their sleep briefly disturbed following each 2 min of accumulated sleep for 2 consecutive nights in 3 different weeks. During 1 week the disturbance was a brief awakening followed by a subjective response. During another week subjects were required to make a quarter-body turn response. During the final week, the disturbance was an ongoing electroencephalographic (EEG) change. As expected, the three disturbance conditions differentially impacted sleep, with the most sleep disturbance seen in the awakening condition and the least disturbance seen in the EEG change condition. Morning vigilance performance and nap latency were decreased and fatigue was increased as compared with baseline following all three disturbance conditions. However, no significant condition interaction was found for any performance variable or for morning nap latency. For the mood scales, significant condition interactions indicated that subjects reported being sleepier only after the awakening condition. The data were interpreted as providing evidence that the restorative function of sleep is equally impaired by any periodic change in ongoing EEG and that impairment does not require a return to waking consciousness. However, mood, as a subjective rating, is dependent upon conscious events that occur during the sleep period.