Chabad Custom Regarding Sleeping in the Sukkah

Chabad custom is to not sleep in the Sukkah, but to be very careful even to drink only in the Sukkah. The Previous Rebbeim did not sleep in the Sukkah; while in the Sukkah he felt the tremendous revelation of the holiness, which kept him from being able to sleep there.

As loyal and dedicated followers of the Rebbeim, Chassidim imitate their behavior; especially since their inability to conduct themselves in a manner similar to their Rebbeim would cause them pain - in turn freeing them from the obligation to sleep in the Sukkah.