The Gemara in Shabbos (151b) rules that it is forbidden to sleep alone in a house. Does this prohibition also apply to sleeping alone in a succah?
The Mishnah (Succah 28a) records a dispute between Beis Hillel and Beis Shammai. Beis Shammai maintains that for a succah to be kosher, it must be large enough to contain a person's head, most of his body, and a table, while Beis Hillel argues that it need only have enough space for his head and the majority of his body. From the fact that Beis Hillel validates a succah which is only big enough for one person to sleep in, the Tchebiner Rav (Shu”t Dovev Meishorim 1:79) deduces that it is permissible to sleep alone in a succah.
The Madanay Asher (Emor 5770) notes that this proof is not ironclad, as Beis Hillel is perhaps referring to a case in which one's succah opens into the house where other people are sleeping. Nevertheless, the Vilna Gaon (Maaseh Rav 221) rules that it is permitted to sleep alone in a succah, as one who is performing a mitzvah will be protected from being harmed.
The Chazon Ish and Steipler Gaon were careful not to sleep alone in a succah (see Orchos Rabbeinu Vol. 2 pg. 224).
