A few years ago I read an interesting book on sleep. (Sorry, I forget the title.) Apparently a lot of interesting experiments have been done on the topic. One point that made an impression on me was some of the research that the military had done on sleep.
The point of their research was how much they could push soldiers and have them remain functional. It turns out that in a stressful situation it turns out that most people can do 48 hour stretch and function all of the way through, but then will crash. It also turns out that most people, when not under pressure, sleep 8-10 hours per night. But if you try you can train them to get by on 6 hours of sleep.
People trained to get by on 6 hours a night show an interesting collection of properties. First of all they claim to be functional. But when people who know them well (eg a spouse) is asked, the spouse says that they are not functional. Judging by the performance on ability tests, the spouses are right and despite the person's self-judgement that they are OK they are impaired.
The issue that when you are running a sleep deficit, one of the first things that is impaired is your self-judgement. With your self-judgement impaired you think you are in far better shape than you are. In today's high-pressure world, most of us most of the time run serious sleep deficits. However a fair amount of research says that if we made a habit of getting enough sleep, we actually will get more done with fewer mistakes!
Well do I know that sometimes this is easier said than done, but keep in mind that heroic efforts often merely lead to heroic mistakes and try to keep up on your sleep...
In reply to Re (tilly) 1: Hours of sleep I get on an average weeknight