As we have seen, it is obligatory to sleep in the sukka, both sheinat keva and sheinat ara’i, yet many are lenient and do not sleep in the sukka. Do they have a basis for their practice? The poskim mention two primary reasons for exemption from sleeping in the sukka. One relates to mitzta’er, and one to married men.
In cold European countries, sleeping in the sukka entailed pain and discomfort because of the cold nights, and people who slept in the sukka would sometimes get sick. Therefore, poskim ruled that if one is mitzta’er vis-à-vis sleeping in the sukka because of the cold, and he has no way to keep warm properly, whether because he does not have enough blankets or because he is mitzta’er even with the blankets, he is exempt from sleeping in the sukka. In Eretz Yisrael it is not that cold, but nowadays there are more spoiled and sensitive people who catch colds easily on chilly nights in the sukka even when they sleep with a heavy blanket. They, too, are deemed mitzta’arim and exempt. However, on nights that they know they will not catch a cold, or when napping in the afternoon, they must sleep in the sukka.[14]
Some people simply cannot fall asleep in a sukka. Even though nothing in the sukka should bother them, they are tense from the different environment. Since, in fact, they cannot fall asleep, they are mitzta’arim and thus exempt. They are not obligated to build a sukka with brick walls so they will feel more comfortable and be able to sleep at night, for the Torah did not command us to build permanent walls to fulfill the mitzva. However, those who do so are commendable, for they will be able to fulfill the mitzva. In addition, one who is unable to sleep in the sukka at night must still sleep in the sukka by day if he wants to take a nap and is able to fall asleep in the sukka during the day.
If one wants to take an afternoon nap, but there are children playing noisily and disturbing him, and they will not manage to keep quiet even if he asks, he is considered mitzta’er. Thus, if he is tired, he may go inside to sleep.[15]
[15]. It is obvious that one who cannot fall asleep in the sukka is exempt because he is considered mitzta’er, although this exemption is limited to situations that would bring most people discomfort. If one is known to be delicate, and all delicate people would be mitzta’er, then he is exempt (Rema 640:5; MB ad loc. 28-29).
If there are guests in the sukka and it would be unpleasant to ask them to leave, one who needs to sleep has the status of mitzta’er and may sleep in the house (Halikhot Shlomo 9:19). Some are lenient in this case only if it would be difficult for him to sleep in a neighbor’s sukka (R. Elyashiv, quoted in Sukkat Ḥayim, p. 435).