Related על סוכה 2:4

Those out on a religious mission are exempt from [the mitzvah of living in] the sukkah, however it is said: "It is no praise for a man to leave his house during the festival." There is a story of Rabbi Ilai, that he went to visit Rabbi Elieser in Lud. He said to him, What does this mean, Ilai? Are you not one of those who rest on the festival? Is it not said, It is no praise for man to leave his house during the festival since it is said, And thou shalt rejoice, thou and thy house?

The sick and their attendants are exempt from observance of the festival ; and not only one who is dangerously ill, but even one who has a headache or a pain in his eyes. Rabbi Simeon ben Gamaliel said: Once I was in Csesarea with pain in my eyes, and R. Jose allowed me and my attendant to sleep outside the sukkah. Rabbi said, "Once I and Rabbi Elieser ben Rabbi Zadok were visiting Rabbi Yohanan ben Nuri at Beth-Shearim, and we were eating figs and grapes outside the sukkah, and Rabbi was saying, 'Every sukkah which is not four cubits square is not valid.'" But the sages say, "If it contains space for the head, and the greater part of the body only, it is valid." There is a story of the men of Jerusalem that they were lowering their beds through windows which were ten handbreadths high, and were sleeping under them. A lath roof prolonged beyond the walls of a sukkah is to be judged like a sukkah.