If one has low spirits because he’s not getting enough sleep and he’s exhausted, is that feeling of unhappiness also considered a sin that he’s accountable for?
Every individual is responsible for his own body – for his or her own health. And therefore everyone must make it their business to get enough sleep. In most cases you can plan your schedule to allow for a program of a proper amount of sleep. Even if your child is up at night, you can plan ahead and get the sleep you need. And don’t waste time at night doing nothing – just fiddling around.
And if you can get someone to take over for a little while every day, you can sleep by day for a half hour. A half hour sleep by day is a yeshu’ah!l Sometime you can sneak in even more than a half hour. But either way, it’s up to you to preserve your health and to remain in good spirits by getting enough sleep. That’s your responsibility.