The shortest I had at one point was 5 hours and never lost energy that day.
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At moments I just did 24 hours without sleep:
-working all night and restarting at 8 pm without hitting my bed.
All work, no fun.
It happened when I was at the university (studying)
and it happened when I was ROTC in the army.(moving , exercising during daylight, moving or going to staf meetings in the middle of the night , happy to find time to eat something between activities.
Later on the job, coming home around 10 or 11pm, eating something, some attention for my wife , a bit at the pc then to bed until 5:30...
One gets used to it.