Please note that the following ideas are condensed summaries extracted from the Sicha. It is essential to study the full Sicha meticulously, considering all the details and nuances for a comprehensive understanding.
There are both Halachic (Jewish legal) and Kabbalistic (Jewish mystical) reasons why Chabad Rebbes and Chasidim have refrained from sleeping in the Sukkah during the holiday of Sukkot.
One reason, as articulated by the Miteler Rebbe, the second Chabad Rebbe, is the profound sense of holiness within the Sukkah. This heightened spiritual atmosphere can make it exceedingly difficult to sleep. In this state, one may be considered "exempt" from the obligation to sleep in the Sukkah while still fulfilling the basic mitzvah by engaging in activities like eating, drinking, and spending time within the Sukkah. This perspective occasionally raises questions about a potential conflict between Halacha and Kabbalah.
Rogatchover, another distinguished Jewish scholar, suggests that while eating must be done in the Sukkah, there is no absolute obligation to sleep within its walls. He points to historical examples, including some of the great Tanaim, who refrained from sleeping in the Sukkah. Their practice underscores the notion that the essence of the Sukkah mitzvah lies in engaging in various activities within its confines. Consequently, those who do not sleep in the Sukkah for various reasons may still be considered to have fully fulfilled the mitzvah of Sukkah.
For many people who do not experience the intense spiritual ambiance of the Sukkah, sleeping is a natural part of their daily routine. However, Chasidim often closely emulate the practices of their Rebbe. If the Rebbe chooses not to sleep in the Sukkah, Chasidim may follow suit out of profound respect and a desire to replicate their Rebbe's actions. To a Chasid, sleeping in a Sukkah while their Rebbe refrains could render them a "Mitztaer" (someone experiencing discomfort), who is "Patur" (exempt) from the obligation of Sukkah.
In cases where someone experiences discomfort or pain in the Sukkah, they are exempt from staying in the Sukkah. This exemption applies not only when the discomfort is caused by the Sukkah itself but also when external factors, such as emulating the Rebbe's practices, come into play.