Did you ever learn the sicha inside? A guilty feeling due to [mis]understanding sisrai Torah has nothing to do with it.
Yes I did, and that’s what it says. Look in the footnote there (62*)
והיינו דנוסף על צערו בכלל ממצבו הירוד [שאינו מרגיש האור המקיף שבסוכה (או שפתגם של אדמור האמצאי אינו פועל עליו כו)] – שמצער זה לא ינצל גם ע”י כניססו לבית – הרי המעשה השינה עצמה גורם לו צער היתכן שיכול לישון בסוכה בלי צער
And it’s the same idea in the Pnim.
In short, the idea is that a Lubavitcher Chossid would feel guilty about sleeping in a Sukkah, since sleeping in a Sukkah forces him out of denial – that he doesn’t feel the Makkif of the Sukkah, even after hearing about it from the Mitteler Rebbe. I can’t speak for everyone (and I personally happen to think that not everyone who wants to call himself Chabad can rely on our leniencies, but that’s for another rant), but I, personally, think that I’d feel guilty sleeping in a Sukkah.
So the Rebbe’s point is that guilt feeling is enough to Patur one from sleeping in a Sukka.