In addition to the quantity of sleep, quality and timing make big differences. Individuals with sleep apnea, for example, with poor sleep quality and fragmented sleep can spend 8 hours "sleeping" and still be nonrestored, as well as suffer a growing catalog of long term consequences in the neurologic, cardiovascular and metabolic domains. Trying to live, or for that matter sleep, out of phase with your circadian rhythm - as for example sleeping 'til noon on weekends and arising (or trying to) at 7am on weekdays - leads to its own significant dysfunction.