I know from personal experience that however long you've stayed up, that 8 hours of sleep is the most you can do to help at that point, in other words after 20

I know from personal experience that however long you've stayed up, that 8 hours of sleep is the most you can do to help at that point, in other words after 20 hours of 'lost sleep' you can really only sleep for 8. (Edit: you can sleep for more but it will make no difference). Or - if you lose a few hours every night during the week, you cannot 'catch up' on the weekend, it doesn't work like that. A person who lives for years at 5 hours a weeknight but 11 on the weekends will be in poorer health than someone who just did 8 hours a night consistently.