Feeling sleep deprived is pretty horrible, and a new study says getting only six hours of sleep can be as bad as getting none at all. Published in the journal Sleep, the study looked at 48 adults and restricted their sleep to a maximum of either, four, six, or eight hours a night for two weeks, while another group was deprived of sleep for three days straight. During their time in the sleep lab, participants were tested every two hours (unless they were asleep) on their cognitive performance and reaction time. They also answered questions about their mood and any symptoms they were experiencing. Results showed those who got to sleep eight hours per night had the highest performance on average. Those who got only four hours a night did worse each day, and those who got six hours each night held their own until around day 10 of the study. The last few days of the study, those who got six hours of sleep per night showed cognitive performances that were as bad as the people who weren’t allowed to sleep at all. In fact, getting only six hours of shut-eye a night was as bad as not sleeping for two days straight. The group that got just four hours of sleep per night performed just as poorly, but they hit their low sooner. Perhaps the most alarming finding–the six-hour sleep group didn’t rate their sleepiness as being all that bad, even as their cognitive performance tanked. The findings raise the question about how people cope when they get insufficient sleep, suggesting they’re in denial about (willfully or not) about their present state.