I have heard of medical students and soldiers in war who go for weeks without solid sleep. How do they do this?

Is there a trick to it? They do not seem to be diminished mentally and continue getting done what needs to be done. Due to life circumstances for the last few months I have been living off broken up sleep and am really feeling it in the form of mental fatigue that does not want to go away.

How do those in stress situations perform so well for so long?

What is the secret?

Is there a certain way to nap that makes a difference? What if you are so wired up from the battle that you cannot achieve deep sleep?

Medical students seem to do well too- and they hold peoples lives in their hands.

Caffeine cannot do it all.