Sleep deprivation impairs performance as much as being drunk

Research by David Dinges at the University of Pennsylvania showed that 17–19 hours without sleep impairs cognitive performance and reaction time to a level equivalent to a blood alcohol concentration of 0.05% — the legal driving limit in many countries. After two weeks of sleeping six hours per night, subjects showed the same deficits as after 24 hours of total sleep deprivation — but critically, they reported feeling only 'slightly sleepy', meaning they had lost the ability to judge their own impairment.

Source: Van Dongen et al., Sleep (2003)