According to reasearch quoted in Wikipedia: "Some researchers argue that the perpetuation of a complex brain process such as REM sleep indicates that it serves an important function for the survival of mammalian and avian species. It fulfills important physiological needs vital for survival to the extent that prolonged REM sleep deprivation leads to death in experimental animals."
Can you get REM sleep on a drug like propofol? Wikepedia's page on propofol doesn't say. And if not, what would be the benefits of being knocked unconscious as a replacement for sleep? Would you still wake up feeling refreshed like you got actual sleep? Or would you eventually die like the experimental animals?