That might be the literal interpretation of what is said, but it's not how I interpreted it. To me there is an implied "in the short term". So if I go without

That might be the literal interpretation of what is said, but it's not how I interpreted it. To me there is an implied "in the short term". So if I go without 4 hours of sleep today, I cannot just choose to sleep an extra 4 (or more) hours tomorrow. It's not an even trade. At some point more sleep has diminishing returns. This does not mean more sleep has no value. Maybe it will add up over the next few days and we'll be back to good. People with sleep deprivation tend to have an REM rebound effect and personally when I've had a few poor nights in a row I will sleep noticeably deeper. If someone is awake multiple days then sleep-like behaviour happens while they are still awake. They start to hallucinate or dream with eyes open, or enter microsleeps that they don't remember. It's not inconveivable to me (personal conjecture warning) that our diminished state is because some of our brain is doing the necessary upkeep normally relegated to sleep, so we're catching up while we are awake. It's just not something we notice until it gets really bad. So, this would remove any permanent cognitive reduction, however you'll probably forever lose any memories that weren't correctly stored and so on.