>When I did my engineering here in India. Preparing for public exams, and entrance exams- I have regularly worked on subjects like Math and Physics almost 15-17 hours a day.
And did you cut this down to (even) 10 hours and observe real changes in productivity?
>Most of it psychological.
No. You get physical symptoms from sleep depredation. You can't think these problems away but you can convince yourself you aren't having them. Doesn't actually change your body's need for sleep.
http://www.webmd.com/sleep-disorders/excessive-sleepiness-10...?
From the article:
Sleep Loss Impairs Judgment, Especially About Sleep
Lack of sleep can affect our interpretation of events. This hurts our ability to make sound judgments because we may not assess situations accurately and act on them wisely.
Sleep-deprived people seem to be especially prone to poor judgment when it comes to assessing what lack of sleep is doing to them. In our increasingly fast-paced world, functioning on less sleep has become a kind of badge of honor. But sleep specialists say if you think you’re doing fine on less sleep, you’re probably wrong. And if you work in a profession where it’s important to be able to judge your level of functioning, this can be a big problem.
“Studies show that over time, people who are getting six hours of sleep, instead of seven or eight, begin to feel that they’ve adapted to that sleep deprivation -- they’ve gotten used to it,” Gehrman says. “But if you look at how they actually do on tests of mental alertness and performance, they continue to go downhill. So there’s a point in sleep deprivation when we lose touch with how impaired we are.”
Sleep plays a critical role in thinking and learning. Lack of sleep hurts these cognitive processes in many ways. First, it impairs attention, alertness, concentration, reasoning, and problem solving. This makes it more difficult to learn efficiently.
Second, during the night, various sleep cycles play a role in “consolidating” memories in the mind. If you don’t get enough sleep, you won’t be able to remember what you learned and experienced during the day.
>You will be surprised how long you can go sleepless, when that is the only option you have
Doesn't mean it's healthy. Doesn't mean that you are performing at max capacity.