You know, I am happy that, even if I am not that rested, I can usually go almost without sleep one night, work a lot, accomplish something next morning or until after lunch and still not feel tired until we're in mid-afternoon. If I don't get to sleep at all, then it's hard on me, but if I can sleep from 2 to 4 hours at night, I usually feel reasonably well the next day. This can be very handy. Now, when the afternoon comes around, if I can't go home and konk out into sleep for a few hours, then I am in trouble. It's that swirling, numbing wave of sleepiness that just sweeps over you again and again and it takes a lot of frustrating effort to keep awake if you absolutely cannot go home to sleep.
Given that I can go to sleep now, I will be OK :-) Sweet dreams to me :-) I will be back in the evening.