Your duty to be virtuous and kind despite feeling horrible is real, but it is your secondary duty. Your first duty is to do what you can to get enough sleep and whatever else you need so you don’t find it so hard to be virtuous in the first place.
In Solomon Says, I wrote a great deal about the temptation to sleep (or “sleep,” since I don’t think only literal unconsciousness is being warned against).
But notice that sleep is also a blessing:
My son, do not lose sight of these—
keep sound wisdom and discretion,
and they will be life for your soul
and adornment for your neck.
Then you will walk on your way securely,
and your foot will not stumble.
If you lie down, you will not be afraid;
when you lie down, your sleep will be sweet.
Proverbs 3:21–24 ESV
So what happens when you get sweet sleep?
To answer that question, lets ask another one: What happens when we are deprived of sleep? We get irritable! “Whoever blesses his neighbor with a loud voice, rising early in the morning, will be counted as cursing” (Proverbs 27:14 ESV). All the virtues Proverbs commends become more difficult with fatigue. It is harder to ignore an insult (12:26) or to stay calm when suffering opposition (29:11).
I assert in Solomon Says that an adult is not defined as being without parenting. Rather, an adult is someone who parents himself. Every parent knows that allowing a child to get inadequate sleep virtually guarantees increased behavioral problems. Being an adult may make you better able to handle times when you are fatigued, but it doesn’t make you impervious to those same problems. No one has an excuse for misbehaving, but fatigue makes it harder to behave in a way that is wise.
Thus, your duty to be virtuous and kind despite feeling horrible is real, but it is your secondary duty. Your first duty is to do what you can to get enough sleep and whatever else you need so you don’t find it so hard to be virtuous in the first place.