For whatever reason I am annoyed by the fact that someone in my life is always tired. No matter how much she sleeps she is always tired and it drives me insane. Her response is always that she is working so much and keeping normal hours compared to me. So this begs the question, do you find sleep necessary or just a luxury? And if its necessary, how much sleep do you need?
Personally, sleep is necessary to a point but anything over that is just cake. With just 4 hours of sleep, I can function normally all day, but I might start to drag towards the end. At 6 hours of sleep I am optimal and never start to drag.
I used to be able to go full tilt for several days without sleep, but those days are gone. On the other ends of the spectrum is my friend who sleeps 2 hours/night maximimum...the rest of the time he is in the physics lab or teaching. Compare that with my friend who gets 12 hours of sleep, gets up for 3 hours and then wants to go back to sleep again. (And no, she isnt ill)