that can vary widely from person to person. and whether not they are trying to stay awake or are having difficulty sleeping. drugs can have a major effect in this area.in general though,at about 72/90 hrs. a person starts to experience visual and auditory hallucinations and the beginings of lack of muscle control. if not yet,soon thereafter a body will experience a trance like state. on occasion a person wil become " too tired to sleep" after long periods of sleep deprivation. I hope this helps.