Experts say there is no definitive answer to this question as of yet because scientists are still working to discover the exact purposes of sleep and its role in the body. Eventually, your body will get tired enough that it will just shut down and go to sleep when given a few moments to relax. Ultimately, it’s a difficult answer not only on the whole, but because individual factors play a role as well. However, the Guinness World Record holder for the longest time without sleep (and no drugs to reduce the feeling of need for it) is Randy Gardner at eleven days—although a Chinese man died after staying awake for a similar period.
After about a day without sleep, your brain stops working normally and starts behaving on a level of impairment similar to that of a blood alcohol level of 0.1% (somewhere in the vicinity of three to eight drinks). The longer you go, the greater those impairments become, as lack of sleep begins to weigh on the brain cognitively, causing everything from memory deficiencies to hallucinations.