The lack of a usual amount of sleep over a given period of time. This is an area of particular interest in the study of the effects of shift work or jet travel on performance. When people are prevented from sleeping they eventually experience ill effects such as hallucinations and confusions of thought and behavior. Some scientists engaged in dream research argue that dreaming is the most important aspect of sleeping and sleep deprivation. Indeed, other than dreaming it is difficult to detect any physiological difference between sleeping and just resting. Note also the similarities to sensory deprivation.