Included in the mitzva of oneg Shabbat is sleeping soundly, as the popular proverb has it: “Sleeping on Shabbat is a pleasure.” But it is not proper for one to sleep on Shabbat in order to work Saturday night. Doing this subordinates Shabbat to the weekday. One should not even sleep on Shabbat in order to study Torah Saturday night, because by doing so he loses precious, holy time on Shabbat, during which Torah study is weightier than learning done during the week (Ben Ish Ĥai, Year 2, Introduction to Shemot, states, based on kabbalistic interpretations, that Torah study on Shabbat is a thousand times more powerful than Torah study during the week. See below, 22:15).
Similarly, it is not proper for one to work extra hours on Thursday and Friday and plan to make up for his lost sleep on Shabbat. On the contrary, it is a mitzva to spend the weekdays preparing for Shabbat. One should prepare food for Shabbat, clean the house, do the laundry, and bathe. Certainly included in Shabbat preparation is making the effort to begin Shabbat in a well-rested state rather than an exhausted one. This allows one to focus on study and prayer and to properly enjoy the Shabbat meals. Only if one worked extra hours on Thursday and Friday due to factors out of his control that left him no other choice may he catch up on sleep over Shabbat, but one may not plan things that way. The saying: “Sleep on Shabbat is a pleasure” means that if one generally sleeps seven hours a night, he should sleep for eight hours on Shabbat, so he will be better rested and refreshed. But it does not mean that Shabbat should, God forbid, become the weekdays’ servant, by serving as a time when people can make up for sleep missed during the week.
In terms of afternoon naps for men, there are various customs. Rambam (MT 30:10) records that pious people would wake up early on Shabbat morning, pray Shaĥarit and Musaf, return home for the second meal, study in the beit midrash until late afternoon, pray Minĥa, and eat se’uda shlishit (the third meal, “shaleshudis”) until the end of Shabbat. However, some poskim write that one who is accustomed to sleep in the afternoon does not have to skip his nap, because sleep is included in oneg Shabbat (Tur §290). Of course, one must be careful that he not sleep so much that he is unable to dedicate time to study. For we have already learned (section1) that on Shabbat at least six hours must be dedicated to Torah study. So, if one sleeps longer on Shabbat afternoon, he must learn more Torah on Friday night after the Shabbat meal or earlier on Shabbat morning.
One must be careful not to eat too much at the meals, because overeating makes people very sleepy and is not truly pleasurable. Though one enjoys the taste of the food while eating, afterward one feels heavy, exhausted, and often also depressed, because all the body’s resources must be mobilized to digest the excessive quantity of food. After eating like this one has no energy to focus on studying or on having deep, beautiful conversation with family members. Therefore one must be very careful not to overeat, so the meal and its delicacies add energy and liveliness to one’s Torah study. One who nevertheless becomes tired after eating should sleep for a bit and then arise energetically to study Torah.